Apparatus and method for pumping supercritical fluid and measuring flow thereof

ABSTRACT

In a piston pump for pumping liquid carbon dioxide at a temperature below 30 degrees Fahrenheit and pressures at least as high as 7500 psi, the volume leaving the pump is determined by measuring only pressure or other parameter related to flow and movement of the plunger. The position of the piston is measured and the resulting displacement is integrated to determine volume of fluid pumped.

RELATED CASE

This application is a division of application Ser. No. 08/208,121, filedMar. 8, 1994, now U.S. Pat. No. 5,635,070, which is acontinuation-in-part application of U.S. patent application Ser. No.08/134,033 filed Oct. 2, 1993, now abandoned, which is a divisionalapplication of U. S. patent application Ser. No. 08/027,257 filed Mar.5, 1993, now U.S. Pat. No. 5,268,103, which is a continuation-in-partapplication of U.S. patent application Ser No. 07/908,458 filed Jul. 6,1992, now U.S. Pat. No. 5,198,197, which is a divisional application ofU.S. patent application Ser. No. 07/795,987 filed Nov. 22, 1991, nowU.S. Pat. No. 5,160,624, which is a continuation-in-part application ofU.S. patent application Ser. No. 07/553,119 filed Jul. 13, 1990, nowU.S. Pat. No. 5,094,753, for APPARATUS AND METHOD FOR SUPERCRITICALFLUID EXTRACTION.

BACKGROUND OF THE INVENTION

This invention relates to supercritical fluid extraction and moreparticularly relates to a reciprocating pump for pumping liquid near itssupercritical temperature in such systems.

In supercritical fluid extraction, an extraction vessel is held at atemperature above the critical point and is supplied with fluid at apressure above the critical pressure. Under these conditions, the fluidwithin the extraction vessel is a supercritical fluid. In one type ofapparatus for supercritical extraction, there is a specially constructedextraction vessel within a source of heat and a specially constructedpump for supplying supercritical fluid to the extraction vessel.

One prior art type of pump used for. supercritical extraction is thesame as a single piston pump used for HPLC. This type of pump hasseveral disadvantages when used for supercritical fluid extraction,which are: (1) a regenerative effect may, under some circumstances, becreated in which the heat of compression increases the temperature ofthe fluid and which in turn increases its compressibility and causes theregenerative effect, which prevents the accurate prediction of flow ratefor purposes of control; (2) the usual cams create destructive reversetorques on the pumping cam, gear train and drive motor after the campasses top dead center because the high compressibility of the liquid inthe pump chamber causes the storing of a relatively high amount ofenergy at high pressures.

Another prior art pump used for supercritical fluid extraction is amultiple cylinder pump of the type now used in HPLC to reduce pulsation.This type of pump, besides being sometimes under some circumstancessubject to the problems of single cylinder pumps, is also more expensiveand complicated.

In still another prior art pump, a cam for driving the piston that is topump a supercritical fluid has a slow return stroke intended to reducedestructive forces. This type of pump has a disadvantage insofar as itcauses pulsations and delays on time during which fluid is notdelivered.

In the prior art pumps, water cooling is usually used or the pumps havevery low flow rates. Other prior art discloses cooling of either theinlet fluid or the pumphead. Such prior art discloses cooling just onebut not the other. In U.S. Pat. No. 5,087,360, there is disclosed asupercritical fluid extraction system in which both the inlet fluid andpumphead are cooled, but water cooling is used for both.

In supercritical fluid extraction pumps, determination of actual fluidflow rate is a significant problem due to the very high compressibilityof fluids used for supercritical applications such as carbon dioxide.The critical temperature of CO₂ is 31.1 degress C., not much above roomtemperature. It is difficult to pump fluids near their critical point, aproblem not encountered with HPLC pumps. The density of theapproximately room temperature liquid (not yet supercritical fluid)leaving the pump is about 11/4 times that of the density of the fluidentering the pump: the compressibility of liquid carbon dioxide is about11/4 to 1 from 870 psi to 7,500 psi. This compressibility is greaterthan the liquids used for HPLC. The high compressibility produces anunfortunate regenerative effect. The heat of compression raises thetemperature of the fluid, which in turn makes it more compressible. Thisin turn raises the heat of compression further. The existence of thisprocess makes a priori accurate prediction of flow rate impossible.

The prior art cams for driving the plunger of a single-plunger pump forpumping highly compressible liquids such as in a liquid fluid supply fora supercritical extractor have a profile similar to that used in highperformance liquid chromatography (HPLC) pumps. However, when using thisprofile highly compressible fluids at high pressure produce anundesirable and possible destructive reverse torque on the pumping cam,gear train and drive motor after the cam passes top dead center. This isbecause the high compressibility of the liquid in the pump chamberresults in the storage of a relatively large amount of energy at highpressure such as 7500 psi.

One conventional solution to this problem is to use a cam with a slowreturn stroke. However, the slow return stroke takes up alot of the camrotation and it is obvious that liquid can not be delivered from thepump during the return stroke. This causes undesirable mechanical stressin and flow pulsations from the single-plunger pump.

Another conventional solution to this problem is to use a two or moreplunger pump as this inherently reduces the pulsations and reduces thereverse torque on the mechanical system since when one head isdepressurizing the other pumphead is delivering and is taking uppositive torque which subtracts from the reverse torque of the pump itis depressurizing. However, this fix is undesirable because adding asecond pumphead decreases reliability because of the increased number ofparts and increases the cost of the pump for the same reason.

SUMMARY OF THE INVENTION

Accordingly, it is an object of the invention to provide a novelsupercritical extraction technique.

It is a still further object of the invention to provide a novelsupercritical extraction apparatus.

It is a still further object of the invention to provide a novel pumpand pumping technique.

It is still further object of the invention to provide a novel techniquefor measuring volumetric flow rate.

It is a still further object of the invention to provide a noveltechnique for controlling the temperature of fluids used insupercritical fluid extraction.

It is a still further object of the invention to provide a novelsupercritical extraction technique which is able to use less expensivecontainers for samples to be extracted than prior techniques.

It is a still further object of the invention to provide a novelsupercritical extraction apparatus and method in which a series ofsamples may be automatically processed with a minimum of handling by anoperator.

It is a still further object of this invention to provide a novelreciprocating pump intended for pumping highly compressible liquids suchas liquid carbon dioxide near its critical point with a minimumpulsation and maximum efficiency and reliability to a pressure of up to7500 psi (pounds per square inch).

It is a still further object of this invention to provide a noveltechnique for pumping highly compressible liquids to pressures up to7500 psi with a single-head pump.

It is a still further object of this invention to provide a noveltechnique for pumping liquid carbon dioxide from a supply vessel at atemperature below 30° and at a pressures as low as the vapor pressure ofthe liquid carbon dioxide at the temperature to a pressure up to atleast 7500 psi without use of a circulating coolant liquid.

It is a still further object of this invention to provide a noveltechnique for pumping highly compressible liquids at a temperature closeto the critical temperature without requiring a fluid coolant loop.

It is a still further object of this invention to provide a noveltechnique for improving the performance of a pump for pumpinghighly-compressible, low-boiling-point fluids by providing both thepumphead and a pump inlet heat exchanger with air-cooled thermoelectriccoolers.

It is a still further object of the invention to provide a noveltechnique for pumping liquid with a temperature near its criticaltemperature to an outlet pressure of at least 7500 psi and an outletflow rate in excess of 10 ml per minute.

It is a still further object of this invention to provide a novelplunger type pump whose plunger is supported concentrically with respectto its seal by a support bearing which lies in the same block of metalas the gland housing the seal.

It is a still further object of the invention to provide a novel meansfor accurately measuring the volume of highly compressible liquid beingpumped to a high pressure.

It is a still further object of this invention to provide a noveltechnique for determining the delivered fluid volume of a pump whichpumps a very compressible liquid to a high pressure and using this knowndelivered fluid volume to form composition gradients by either highpressure or low pressure mixing of two or more fluids.

It is a still further object of the invention to provide a novel liquidCO₂ pump that pumps liquid CO₂ from a reservoir pressurized only by thevapor pressure of the liquid CO₂ without the use of helium overpressurein the reservoir to a higher pressure suitable for supercritical fluidextraction.

In accordance with the above and further objects of the invention, asupercritical fluid extraction system includes a cartridge capable ofholding the sample to be extracted, a pressure vessel into which thecartridge fits, a pumping system and a collection system. The pressurevessel fits into a heater and the cartridge is removably mounted to abreech plug that seals the pressure vessel. There are separate outletsfor the cartridge and pressure vessel to permit equalization of pressureon the inside and outside of the cartridge without contamination fromimpurities outside the cartridge but inside the pressure vessel. Aspecially designed pump for the supercritical extraction system is acam-driven single-plunger pump having a cam profile that enables thepumping system to avoid destructive reverse torque on the cam, geartrain and drive motor after the cam passes top dead center.

The fluid volume leaving the pump is determined by measuring onlypressure or other parameter related to flow and movement of the plunger.Measurement of the fluid volume leaving the pump is useful for recordingor indicating the flow rate while the pump is operating as follows: (a)recording or indicating the flow volume or flow rate of the pump whenthe pump is operating at constant pressure; and (b) useful as feedbackmeans for controlling the pump to provide constant flow.

The fluid delivery volume or actual flow rate provides signals used foraccurate formation of either high pressure (outlet side) or low pressure(inlet side) composition gradients.

The pumphead and the inlet fluid are air-thermo-electrically cooledseparately and simultaneously. It is surprising that air heat rejectionis satisfactory as previous designs are water cooled or have very lowflow rates. Also, there are surprising advantages over cooling just onebut not the other as described in prior literature.

The plunger or piston of the pump is supported on both sides of the sealto lengthen the seal life by improving the alignment of the plungerwithin the seal. The plunger support within the pumphead is thecontrolling locator of the seal and is machined concentric and collinearto the seal gland. This construction which increases seal life isparticularly useful because pump head cooling makes seal replacementmore difficult.

In an automatically operated supercritical fluid extraction,programmable valves are caused to open and close to control the flow ofhigh pressure fluids into the pressure chamber of a supercritical fluidextractor. For this purpose, a valve is provided having a valve seatthat receives a spherical or ball-shaped valve element and a valve stemthat is moved reciprocally to force the valve element into the seat orto release it. The ball is free to rotate upon being released and thesupercritical fluid flows past the ball through the seat and into thepressure vessel.

In the preferred embodiment, the reciprocating stem that forces thevalve element to close or releases it is controlled by a programcontrolled rotary motor. The reciprocating stem is connected to a rotaryelement that moves up and down to move the stem but does not cause thestem to rotate with it but only causes it to reciprocate.

To automate the operation under the control of a microprocessor, a motoroperated fraction collector, a motor operated sample source and a motoroperated sample injector automatically move samples and collectioncontainers into an extraction station, inject samples into theextraction pressure vessel, perform extraction and collect extractant indifferent appropriate collection containers in a timed sequence topermit extracting of a series of samples with minimum human handling.

In the preferred embodiment, a movable motor member is aligned: (1) withan opening in a sample cartridge reel that moves sample cartridgescarrying samples into the extraction station; and (2) with an opening inthe extraction pressure vessel. The movable member is dimensioned to becapable of sealing a correspondingly sized opening in the pressurevessel and adapted to move the sample cartridge into the pressure vesseland seal the pressure vessel.

As can be understood from the above description, the supercriticalextraction technique has several advantages, such as for example: (1) itis more convenient than prior art extractors; (2) it automates thesample injection and fraction collection part of the extraction processas well as automating the extraction itself; (3) it is smaller and morecompact becuase of the air-thermoelectric cooling the pumphead and theinlet fluid separately and simultaneously; (4) it may have a reasonablyhigh flow rate; (5) seal life is lengthened by improving the alignmentof the plunger within the seal; (6) fluid volume leaving the pump isprecisely measured; and (7) no water cooling is required.

DESCRIPTION OF THE DRAWINGS

The above noted and other features of the invention will be betterunderstood from the following detailed description when considered withreference to the accompanying drawings in which:

FIG. 1 is a schematic diagram illustrating the operation of a singlesupercritical fluid extraction system according to the invention;

FIG. 2 is a fragmentary sectional view of the extraction cartridge,breech plug pressure vessel and heating block;

FIG. 3 is a perspective view of another embodiment of the inventioncapable of automatic extraction of a series of samples;

FIG. 4 is a sectional view taken through lines 4--4 of FIG. 3;

FIG. 5 is a sectional view taken through lines 5--5 of FIG. 4;

FIG. 6 is a sectional view taken through lines 6--6 of FIG. 5;

FIG. 7. is a cross-sectional, fragmentary view of the pumphead, itsdrive cam, thermoelectric cooling means;

FIG. 8 is an elevational view of two supercritical cams showing thedifference between a drive cam of an HPLC pump and the cam of thisinvention;

FIG. 9 is a developed curve illustrating the difference between a drivecam of an HPLC pump and the drive cam of the pump of this invention;

FIG. 10 is a sectional fragmentary view of the fluid inlet heatexchanger;

FIG. 11 is a fragmentary elevational view of the metal pumphead, thein-line heat exchanger assembled to thermoelectric cooling means and afan which removes rejected heat from the thermoelectrical-cooling means;

FIG. 12 is an elevational view of the pumphead including its drive cam,support bearings for the drive cam, a reduction gear box and an electricdrive motor and position transducers which constitutes the pumping unitand its drive mechanism;

FIG. 13 is a schematic view of the pumping mechanism of the subjectinvention;

FIG. 14 is a schematic circuit diagram of a control circuit useful inthe embodiment of FIG. 13;

FIG. 15 is a schematic diagram of the constant flow controller forcontrolling the pump motor speed of the subject invention;

FIG. 16 is a block diagram of the flow rate indicator/controller used todetermine the actual flow rate for the constant pressure operation ofthe subject invention;

FIG. 17 is a schematic diagram of the gated flow pulse generator andflow rate indicator controller of the subject invention;

FIG. 18 is a cross-sectional elevational view of a valve useful in theinvention;

FIG. 19 is a block diagram of the circuitry for operating the system;

FIG. 20 is a schematic circuit diagram of a portion of the block diagramof FIG. 19; and

FIG. 21 is a schematic circuit diagram of another portion of the blockdiagram of FIG. 19.

DETAILED DESCRIPTION

In FIG. 1, there is shown a schematic fluidic diagram of one channel ofa dual-channel supercritical fluid extraction system 10 having a pumpingsystem 12, a valve system 14, a collector system 16 and a pressurevessel and fluid-extraction assembly 18. The pumping system 12communicates with two extraction cartridges within the pressure vesseland fluid-extraction assembly 18 and for this purpose is connectedthrough a tee joint 20 to two identical valve systems, one of which isshown at 14. Each valve system communicates with a different one of twoinlets for the corresponding one of two extraction cartridges.

A specially designed pump (not shown in FIG. 1) for the supercriticalextraction system is a cam-driven single-plunger pump having a camprofile that enables the pumping system to avoid destructive reversetorque on the cam, gear train and drive motor after the cam passes topdead center.

The fluid volume leaving the pump is determined by measuring onlypressure or other parameter related to flow and movement of the plunger.Measurement of the fluid volume leaving the pump is useful for recordingor indicating the flow rate while the pump is operating as follows: (a)recording or indicating the flow volume or flow rate of the pump whenthe pump is operating at constant pressure; and (b) useful as feedbackmeans for controlling the pump to provide constant flow.

The fluid delivery volume or actual flow rate provides signals used foraccurate formation of either high pressure (outlet side) or low pressure(inlet side) composition gradients.

The pumphead and the inlet fluid are air-thermo-electrically cooledseparately and simultaneously. It is surprising that air heat rejectionis satisfactory as previous designs are water cooled or have very lowflow rates. Also, there are surprising advantages over cooling just onebut not the other as described in prior literature.

The plunger or piston of the pump is supported on both sides of the sealto lengthen the seal life by improving the alignment of the plungerwithin the seal. The plunger support within the pumphead is thecontrolling locator of the seal and is machined concentric and collinearto the seal gland. This construction which increases seal life isparticularly useful because pump head cooling makes seal replacementmore difficult.

The valve system 14 and a second valve system (not shown in FIG. 1)which is connected to the other branch of the tee joint 20 are eachconnected to two different collector systems 16, one of which is shownin FIG. 1, and to different ones of the two extraction cartridges in thepressure-vessel and fluid-extraction assembly 18 so that, two extractionoperations can be performed at the same time using the same pumpingsystem 12. With this arrangement, the valve system 14 causes: (1)supercritical fluid to flow from the pumping system 12 into a spacebetween a cartridge and the interior of the pressure vessel of thepressure-vessel and fluid-extraction assembly 18 for purging the outsideof the cartridge and the inside of the pressure vessel; and (2) appliessupercritical fluid through the cartridge for extraction of a sample 134therein. Because the fluid is applied both to the interior of thecartridge and the exterior, the cartridge does not have to withstand ahigh pressure difference between its interior and exterior and can bemade economically.

In addition to controlling the flow of fluid into the pressure-vesseland fluid-extraction assembly 18, the valve system 14 controls the flowof: (1) purging supercritical fluid from the space between the cartridgeand interior of the vessel to the collector system 16 or to a vent; and(2) the extractant from the interior of the cartridge to the collectorsystem 16 for separate collection.

To hold sample 134 during an extraction process, the pressure-vessel andfluid-extraction assembly 18 includes a heating block 22, a pressurevessel 24 and a cartridge and plug assembly 26 with the cartridge andplug assembly 26 extending into the pressure vessel 24. The pressurevessel 24 fits within the heating block 22 for easy assembly anddisassembly. With this arrangement, the heating block 22 maintains thefluids within the pressure-vessel and fluid-extraction assembly 18 atsupercritical fluid temperature and pressure for proper extraction.

The cartridge and plug assembly 26 includes an extraction cartridgeassembly 30, a breech plug 32 and a knob 34 which are connected togetherso that: (1) the pressure vessel 24 is easily sealed with the breechplug 32; (2) the extraction cartridge assembly 30 snaps onto the breechplug 32 and the assembly may be carried by the knob 34; and (3) the knob34 serves as a handle to insert and fasten the assembly to the tubepressure vessel with the extraction tube communicating with an outletaligned with its axis and an inlet for the space between the internalwalls of the pressure vessel 24 and the exterior of the extractioncartridge 30 and for the interior of the extraction cartridge 30 beingprovided through a groove circumscribing the assembly inside thepressure vessel 24.

With this arrangement the extraction cartridge assembly 30 may be easilysealed in the pressure vessel 24 by threading the breech plug 32 into itand may be easily removed by unthreading the breech plug 32 and liftingthe knob 34. The extraction cartridge assembly 30 contains a hollowinterior, an inlet and an outlet so that a sample to be extracted may beplaced in the hollow interior and supercritical fluid passed through theinlet, the hollow interior and to the outlet to a collector. Theextraction cartridge assembly 30 serves as an extraction chamber ortube, the pressure vessel 24 serves as an extraction vessel and theheating block 22 serves as an oven as these terms are commonly used inthe prior art.

In the preferred embodiment, the knob 34 is of a low heat conductivitymaterial and it should include in all embodiments at least a heatinsulative thermal barrier located to reduce heating of the handleportion of the knob 34. It extends outside of the pressure vessel 24 andis adapted to aid in the sealing of the pressure vessel 24 and thebreech plug 32 together so that the extraction cartridge assembly 30 iswithin the pressure vessel 24 for maintaining it at the appropriatetemperature and the knob 34 is outside the pressure vessel 24 so as toremain cool enough to handle.

Although in the preferred embodiment the knob 34 is a heat insulativematerial, it only needs to be insulated against heat conducted from theinterior of the pressure vessel 24 and this may also be done by athermal barrier separating the pressure vessel 24 from the knob 34 suchas an insulative disc having a width of at least 1 millimeter andextending across the cross-section of the knob 34 to the extent of atleast 80 percent of the cross-section to effectively block anyconsiderable amount of transfer of heat between the cartridge and theknob 34. It should have a heat conductivity no greater than 0.05calories/cm. sec. degree C. at 30 degrees Centigrade.

The extraction cartridge assembly 30 has an opening which permits somesupercritical fluid to enter the pressure vessel 24 to follow one pathpassing into the extraction tube and out through an outlet of theextraction tube into a conduit leading to a collector. Othersupercritical fluid follows a second path around the outside of thecartridge to remove contaminants from the pressure vessel 24, equalizepressure and flow from another outlet. One of the inlet and outlet ofthe extraction cartridge assembly 30 enters along the central axis ofthe extraction cartridge assembly 30 and the other from the side topermit rotation of parts with respect to each other during seating ofthe pressure vessel 24 and yet permit communication of the extractioncartridge assembly 30 with the fluid source and with the collector. Toreduce wasted heat and fluid, the space between the outside of thecartridge and the inside walls of the pressure vessel 24 is only largeenough to accommodate the flow of purging fluid and to equalize pressurebetween the inside and outside of the cartridge. The volume between theoutside of the cartridge and the inside of the pressure vessel 24 isless than 10 cubic centimeters.

In the preferred embodiment, the inlet opens into an annular spacebetween the internal wall of the pressure vessel 24 and the cartridgeand plug assembly 26. The fluid follows two paths from the annularspace, both of which include an annular manifold with narrow holes and apassageway that communicates with the recess in the breech plug 32. Onepath opens into the extraction cartridge assembly 30. The other passesalong the narrow space outside the extraction cartridge assembly 30.Thus, supercritical fluid enters the extraction tube through alabrythian like path and at the same time passes outside the extractiontube so that the pressure inside the extraction tube is alwayssubstantially the same as that inside the pressure vessel 24. Becausethe pressures are substantially the same, the tube itself may be formedof relatively inexpensive plastics notwithstanding that a high pressureis desirable for extraction from the sample within the extraction tube.

The pressure vessel 24 is generally formed of strong material such asmetal and is shaped as a container with an open top, an inlet openingand two outlet openings. The inlet opening is sized to receive an inletfitting 42, the inlet fitting 42 being shown in FIG. 1 connected inseries with check valve 60A to corresponding heat exchanger 40. Each ofthe two outlet openings are sized to receive a different one of acorresponding purge valve fitting 44, and a corresponding extractantfluid fitting 46. With these fittings, the pressure vessel 24 is able toreceive the cartridge and plug assembly 26 in its open end and permitcommunication between the cartridge and the extractant fluid fittingssuch as shown at 46. The inlet fittings such as shown at 42 and purgevalve fitting, such as 44, permit communication with the inside of thepressure vessel 24.

To control the flow of fluids to and from the pressure vessel andfluid-extraction assembly 18, the valve system 14 includes an extractantvalve 50, a purge fluid valve 52 and an extracting fluid valve 54.

To introduce extracting fluid into the pressure-vessel andfluid-extraction assembly 18, the extracting fluid valve 54 communicateswith one branch of the tee joint 20 through tube 56 and with one end ofthe heat exchanger 40 through tube 58, the other end of the heatexchanger 40 communicating with the inlet fitting 42 through tube 60,check valve 60A and tube 60B. With these connections, the extractingfluid valve 54 controls the flow of fluid from the pumping system 12through the heat exchanger 40 and the pressure vessel 24 through theinlet fitting 42.

To remove purge fluid from the pressure vessel 24, the purge fluid valve52 communicates at one port with the purge valve fitting 44 through tube62 and with its other port through tube 64 (not shown in FIG. 1) withthe collector system 16 or with a vent (not shown) to remove fluidcontaining contaminants from the exterior of fluid extraction cartridgeassembly 30 and the interior of the pressure vessel 24.

To remove extractant from the extraction cartridge assembly 30, theextractant valve 50 communicates at one of its ports through tube 66with the extractant fluid fitting 46 and through its other port with thecollector system 16 through tube 68 for the collecting of the extractedmaterial, sometimes referred to as analyte or extractant, from thesample within the pressure vessel and fluid-extraction assembly 18.

For convenience, the valves 52 and 54 are mounted to be operated by asingle manual control knob 70. To supply fluid to the valve system 14:(1) the tube 76 carries pressurized fluid from the pumping system 12 totee joint 20; (2) another tube is connected to the top arm of tee joint20 to carry pressurized fluid to another liquid extraction system unitnot shown on FIG. 1; and (3) the remaining arm of the tee joint 20 isconnected through the tube 56 to an inlet fitting 74 of extracting fluidvalve 54. The valves 50, 52 and 54 may be SSi type 02-0120.

The extracting fluid valve 54 has a rotary control shaft 80 that isrotated to open and close its internal port. This shaft is operated byhand control knob 70 and carries spur gear 82 pinned to the controlshaft 80. Spur gear 84, which is pinned to control shaft 107 of purgefluid valve 52, meshes with spur gear 82 so that when control knob 70 isrotated clockwise, extracting fluid valve 54 is closed, but since thecontrol shaft 107 of purge fluid valve 52 is geared to turn in theopposite direction, the clockwise rotation of knob 70 opens purge fluidvalve 52.

The relative locations of the two gears on the two shafts are such that,in the first (clockwise) position of the knob 70, the extracting fluidvalve 54 is shut and the purge fluid valve 52 is open. Turning thecontrol knob 70 counterclockwise 130 degrees from this first positionopens extracting fluid valve 54 while allowing purge fluid valve 52 toremain open. Thus, both valves are open when the knob 70 is rotated 130degrees counterclockwise from the first position. When the knob 70 isrotated 260 degrees counterclockwise from the first position, extractionfluid valve 54 is open and purge fluid valve 52 is shut. Thus, there arethree definable positions for control knob 70: (1) clockwise with valve54 shut and valve 52 open; (2) mid position with both valves open; and(3) full counterclockwise with valve 54 open and valve 52 shut.

The extractant valve 50 includes an inlet fitting 120, outlet fitting122, manual control knob 132 and control shaft 126. The rotary controlshaft 126 is attached to control knob 132. When the extractant valve 50is opened by turning the control knob 132 counterclockwise from itsclosed position, fluid flows from the extraction cartridge assembly 30,through the extractant fluid fitting 46, the conduit 66, the valve inletfitting 120, the outlet fitting 122, through the tube 68 and into thecollector system 16.

The collector system 16 includes a purge coupling 90, a purge fluidcollector 92, an extractant coupling 94, an analyzing instrument 96, andan extractant fluid collector 98. The purge fluid flowing through thevalve 52, flows through purge coupling 90 into the capillary tube 110and from there into the purge fluid collector 92 where it flows into asolvent 100. Similarly, the extractant flowing through valve 50 flowsthrough tube 68 to the extractant coupling 94 and from there to thecapillary tube 128 and extractant fluid collector 98 which contains anappropriate solvent 104 in the preferred embodiment.

The analyzing instrument 96 may be coupled to the capillary tube 128through an optical coupling 102 in a manner known in the art. Theoptical coupling 102 is a photodetector and light source on oppositesides of a portion of the capillary tube 128, which portion has beenmodified to pass light. This instrument 96 monitors extractant and mayprovide an indication of its passing into the extractant fluid collector98 and information about its light absorbance. Other analyticalinstruments may also be used to identify or indicate othercharacteristics of the extractant.

In FIG. 2, there is shown a sectional view of the clipped-togetherextraction cartridge 26, knob 34 and breech plug 32 replaceablyinstalled in pressure vessel 24 which in turn has previously beenpermanently force fit into heating block 22. The pressure vessel 24 isfabricated of type 303 stainless steel for good machinability andcorrosion resistance and has within it a cylindrical central openingsized to receive the extraction cartridge 26, two openings for outletfittings in its bottom end, an opening in its cylindrical side wall toreceive an inlet fitting and an open top with internal threads sized toengage the external threads 188 of the breech plug 32. The heating block22 is fabricated from aluminum for good thermal conductivity andincludes a cylindrical opening sized to tightly receive the pressurevessel 24. The breech plug 32 and the extraction cartridge assembly 30are a slip fit within the pressure vessel 24. External threads 188 onbreech plug 32 engage in internal threads 200 within pressure vessel 24.

An annular self-acting high pressure seal 202 cooperates with a sealingsurface 186 to seal high pressure supercritical fluid from theatmosphere and an annular low pressure seal 204 spaced from the annularhigh pressure seal 202 prevents contaminated supercritical fluid in thespace between the interior of the pressure vessel 24 and the exterior ofthe extraction cartridge assembly 30 from getting back to thesupercritical fluid supply. These two annular seals 202 and 204 formbetween them a toroidal inlet chamber into which the outlet of the fluidinlet 42 extends to introduce fluid. Contamination may arise fromfingerprints or other foreign material on the outside wall of extractioncartridge assembly 30 and the low pressure seal 204 protects againstthis contamination. Seals 202 and 204 are Bal-Seal type 504MB-118-GFP.

Supercritical fluid is supplied to fluid inlet 42 and circulates in theannular space between high pressure seal 202 and low pressure seal 204,and then follows two paths into the pressure vessel 24 and extractioncartridge 30: one path for purging and one path for extraction. Anannular spacer 206 within the torroidal opening between seals 202 and204 has an hour-glass shaped cross section with radial holes through itand distributes incoming supercritical fluid from the inlet of fitting42 to the opposite side of the spacer 206 from which it flows topassageway 208 drilled in breech plug 32.

Because the passageway 208 extends radially from the recess 180 in thebreech plug 32 to the annular ring, it provides an open path for fluidbetween the two regardless of the orientation of passageway 208. Thepassageway 208 opens at an uncontrolled angular location with respect tothe inlet fixture 42 (inner side). Fluid flows from one side of theinwardly curved portion of the hour glass shaped spacer 206 thatcommunicates with the outlet of fitting 42 to the other side of theinwardly curved portion and from there to the passageway 208.

When the cartridge and plug assembly 26 are inserted into the pressurevessel 24 as shown in FIG. 2, the knob 34 is rotated and the externalthreads 188 of the breech plug 32 which form an eight, thread per inchconnector engage internal threads 200 in the pressure vessel 24,screwing the breech plug 32 and attached cartridge and plug assembly 26down into the pressure vessel 24. When conical recess 210 in the bottomcap 144 reaches the external conical tip 212 of fitting adapter 214, thecartridge and plug assembly 26 is prevented from moving further down.

Screwing the breech plug 32 in further after the cartridge and plugassembly 26 has bottomed causes the upper flat annular surface offitting nipple 176 to bear upon the flat lower surface of a hat-shapedwasher 216. At this time, the hat-shaped washer 216 is residing againstthe upper surface of the head of a shoulder screw 218 which is threadedinto cylindrical hole 222 in breech plug 32.

Further screwing of the breech plug 32 into the pressure vessel 24causes the nipple 176 to lift the washer 216 off of the screw head andcompress a coil spring 201 between annular surface 205 and the ridge ofthe washer 216. Continued screwing of the breech plug 32 into thepressure vessel 24 causes annular flange 190 of breech plug 32 to bearupon the upper surface of the pressure vessel 24. This provides a limitstop with the coil spring 201 compressed, as shown in FIG. 2.

The force of the compression spring 201 is enough to provide a lowpressure seal between the hat-shaped washer 216 and the upper annularsurface 203 of the fitting nipple 176. More importantly, this force alsoprovides a low pressure seal on the mating concical surfaces of therecess 210 of lower cap 144 and the external conical tip 212 of thefitting adapter 214.

The sealing surface 186 acts as a pilot during the initial part ofinsertion to insure that the internal threads 188 do not getcross-threaded. A taper 189 at the end of the cylindrical sealingsurface 186 pilots the breech plug 32 past seals 202 and 204 so thatthey are not damaged during insertion of the breech plug 32.

The locations of recess 224, passageway 208, high pressure seal 202 andthe engaging threads 188 and 200 are chosen such that if the breech plug32 is inadvertently removed when the interior of the pressure vessel 24is pressurized, fluid within the pressure vessel 24 leaks past highpressure seal 202 and runs up the flights of the engaging screw threads188 and 200, and depressurizes the system while there is still adequatescrew engagement to ensure safety at the maximum rated operatingpressure. The maximum rated operating pressure of the embodiment shownin FIG. 2 is 10,000 psi. The maximum operating temperature is 150degrees Centigrade. The equipment need not be designed for operatingtemperatures above 300 degrees Centigrade and pressure above 30,000pounds per square inch.

After the breech plug 32 and the cartridge and plug assembly 26 areassembled into the pressure vessel 24 as described above, but before anextraction, the space between the cartridge and plug assembly 26 and thepressure vessel 24 is purged of contaminants. During such a purge orcleaning cycle supercritical fluid enters fluid inlet 42, is distributedby the annular spacer 206 and goes through passageway 208. It passesbetween the outer diameter of hat-shaped washer 216 and the insidecylindrical diameter 230 of the recess within breech plug 32. Fluid thencontinues down and passes the annular space between the outside diameterof engaging nipple 176 and inside diameter 230 of the recess 180 inbreech plug 32. The fluid passes garter spring 184 and circulates witheven circumferential distribution around the outside of top cap 148, theextraction tube 152, and the bottom cap 144. The flow is collected inthe annular space below the bottom cap 144 and above the bottom 240 ofpressure vessel 24 and exits through vent discharge fitting 44, carryingcontaminants with it.

Contaminated fluid between the exterior of extraction cartridge 26 andthe interior of high pressure vessel 24 does not make its way into theinterior of the extraction vessel. Low pressure seal 204 preventscontaminated fluid from reaching passageway 208. A labyrinth sealconsisting of the narrow gaps between the major diameter of fittingnipple 176 and the inside diameter 230 of recess 180, and between insidediameter 230 and the outside diameter of the hat-shaped washer 216,prevents contaminants from reaching the space above the hat-shapedwasher 216 by diffusion.

During a purge or cleaning cycle, there is downward flow ofsupercritical fluid through these gaps, and since the gaps are small,this downward fluid flow prevents eddies of contaminated fluid frompassing up through the gaps. These gaps are only a few thousandths of aninch. Because the top of nipple 176 and the conical recess 210 at thebottom of the extraction cartridge are sealed by spring pressure,contamination cannot enter in these ways.

For extraction, supercritical fluid entering fitting 42 is distributedin the space occupied by spacer ring 206, flows through passageway 208and flows down the few thousandths of an inch radial gap between theshoulder of shoulder screw 218 and the inside diameter of washer 216.The fluid continues to flow down and flows through passageway 250,porous frit 162 and into extraction volume 254 where it passes throughmaterial to be extracted. Extraction volume 254 is shown sized in FIG. 2for a 10 cubic centimeter volume to receive sample. After passing theextraction volume fluid, it is exhausted for sample collection throughfrit 160, passageway 260, fitting adapter 214 and out through fitting46.

All tubing, except tubing designated as capillary tubing, in thisdisclosure is 300 series stainless steel with an outside diameter of1/16 inch and inside diameter 0.02 inch.

In operation after assembly, the fluid flow associated directly with thepure fluid valve 54 (FIG. 1) exiting its port 114 (FIG. 1) flows throughtube 58 through the heat exchanger 40, which is formed by coiling acontiguous segment of tubing into a helix, through the check valve 60Aand through the tube 60B to the inlet fitting 42 of pressure vessel 24.The heat exchanger 40 actually resides in a longitudinal bore throughheating block 22 so that the heat exchanger is at the same temperatureas pressure vessel 24 and extraction tube 30. This preheats any fluidflowing into inlet fitting 42 to essentially the same temperature as theextraction cartridge assembly 30. This temperature is above the criticaltemperature for the fluid. Assuming that the pump 12 is set to produce aconstant fluid pressure greater than the critical pressure, fluidentering the pressure vessel 24 will be a supercritical fluid.

The check valve 60A prevents backflow of supercritical fluid out of thepressure vessel 24 and extraction cartridge 26 of a first channel of adual channel supercritical extraction system if there is a momentarydrop in pressure of the supercritical fluid at the location of the tee20. Such a pressure fluctuation could occur if the second channel of adual channel extraction system is suddenly purged while the firstchannel is extracting. Each channel requires such a check valve.

During a purge cycle, contaminated supercritical fluid leaves fitting44, flows through a tube 62 and enters the inlet fitting 116 of thepurge fluid valve 52. Then it exits the outlet fitting 118 and passesthrough the tube 64 to the coupling 90 (FIG. 1). The coupling 90 couplesthe quartz capillary tube 110 so that contaminated purge gas exitsthrough it. The bore of the capillary tube is small enough, such as 75micrometers, and its length long enough, on the order of a few inches,to provide enough fluid resistance to limit the flow to a convenientrate: for example 5 milliliters per minute with respect to displacementof pump 12, at a pressure of 3,000 psi. Pump 12 is a constant pressurepump so this fluid flow does not affect the pressure within pressurevessel 24 once the flow stabilizes.

The outer end of capillary 110 may be immersed a purge fluid collector92 (FIG. 1) containing an appropriate solvent 100 such as isopropylalcohol to serve as a collector. Bubbles through this solvent indicateproper flow and the solvent tends to prevent the end of the capillarytube 110 from being plugged by the exhausted contaminants. A solvent ischosen in a manner known in the art to dissolve contaminants so the endof the capillary tube 110 does not plug and so the solvent may later beanalyzed if desired to determine whether there was any contaminants onthe exterior of the extraction cartridge.

During an extraction cycle, extractant exits fitting 46 on pressurevessel 24 and passes through tube 66. This tubing extends to inletfitting 120 of extractant valve 50 which has rotary control shaft 126attached to control knob 132. When the extractant valve 50 is opened byturning it counterclockwise from its closed position, fluid exits fromits fitting 122, through tube 68 to fitting 94. Fitting 94 couples toquartz capillary tube 128 or other flow restrictor device.

Capillary tube 128 has a small enough bore, such as 50 micrometers, anda long enough length, on the order of several inches, to produce a flowrate, relative to the displacement of constant pressure pump 12, of aconveninent amount. For example, this may be two milliliters per minute.The end of the capillary tube 128 dips into solvent 104 in theextractant collector 98.

Isopropyl alcohol is under some circumstances used for solvent 104. Thissolvent 104 must be a good solvent for the extractant since it must trapthe extractant by dissolving it from the gas bubbling through it andmust prevent plugging at the end of the capillary tube 128.

The solvent 104 is removed after extraction and is analyzed to determinethe composition and amount of the extractant. Because of the pressureand temperature drop along the length of capillary 128 (and alsocapillary 110) fluid entering the capillary as a supercritical fluid (ora liquid if fitting 90 or fitting 94 is not heated) changes to a gas bythe time it reaches the far end where it dips into the solvent which isat room temperature.

Before using the extraction system 10, the pump 12 is set to the desiredpressure and the heater block 22 is set to the desired temperature. Thebottom cap 144 (FIG. 2) with the frit 160 is screwed onto the bottom ofextraction tube 152. The internal cavity 158 is then filled or partlyfilled with sample to be extracted. The frit 162 and top cap 174 arethen screwed on to the top of extraction tube 152 forming the cartridgeand plug assembly 26. The cartridge and plug assembly 26 is then clippedinto breech plug 32 by shoving the fitting nipple 176 on the extractioncartridge past garter spring 184 located within breech plug 32. Knob 70is set to the vent position closing valve 54 and opening valve 52 (FIG.1). Valve 124 is set to the clockwise closed position.

The assembled breech plug and extraction cartridge are inserted intopreheated pressure vessel 22 and manually screwed with knob 34 intopressure vessel 24 until annular flange 190 contacts the top of pressurevessel 24 (FIG. 2). The pressure vessel has been preheated under controlof a thermocouple temperature controller to the desired temperature. Thecartridge and plug assembly 26 within pressure vessel 24 rapidly risesto the required temperature.

After insertion of the cartridge and plug assembly 26 into the sampleblock 24, valve knob 70 is rotated to the purge position. In thisposition, both valves 54 and 52 are open. Since the pump 12 has alreadybeen set to the desired fluid pressure, fluid flows through tubes 76,56, valve 54, tube 58, heat exchanger 40, tube 60, check valves 60A and60B and inlet fitting 42 into the cavity 180. Since valve 124 is closed,supercritical fluid preheated to the correct temperature by heatexchanger 40, flows past hat-shaped washer 216, fitting nipple 176 andaround the outside of cartridge and plug assembly 26. This supercriticalfluid dissolves any contaminants on the outside of extraction cartridgeassembly 30 and any contaminants inside pressure vessel 24. The hotsupercritical fluid also insures that the extraction cartridge assembly30 is at the proper operating temperature. The supercritical fluidflushes the contaminants from fitting 44, through tube 62, valve 52,tube 64, the fitting 90 and the capillary tube 110.

After a short purge cycle, control knob 70 is set to the extractposition. This sets valves 54 and 52 so that valve 54 is open and valve52 is closed. Immediately after making this setting, the operator opensvalve 124 by rotating knob 132 counterclockwise in the extractdirection. Pressurized fluid flows through valve 54 into heat exchanger40 so that it is at the desired supercritical temperature, and flowsinto fitting 42. It then flows into cavity 180 and past the annularspace between shoulder screw 218 and the inside diameter of hat-shapedwasher 216, after which it passes through the interior of fitting nipple176, through passageway 250 and into the extraction vessel 26. Thissupercritical fluid flowing through the interior sample cavity 254 ofthe extraction cartridge extracts analyte from the sample 134 containedwithin the cavity 254.

Supercritical fluid with the analyte in solution passes out through thefitting 46, the tube 66, the valve 124, the tube 68, the coupling 94 andthe capillary tube 128 which leads into the collecting solvent 104within test tube 98. The analyte is dissolved in the solvent 104 forlater analysis. When the extraction is complete, knob 132 is rotatedclockwise in the closed direction, closing valve 124. This stops theflow of supercritical fluid into the extraction cartridge 26. Knob 70 isthen rotated clockwise to the vent position. This closes valve 54 andopens valve 52, depressurizing the pressure vessel 24 and cartridge andplug assembly 26 through capillary tube 110.

When bubbles stop issuing through the end of capillary tube 110,depressurization is complete. Knob 34 is rotated counterclockwise tounscrew the breech plug 32 and the attached cartridge and plug assembly26 from pressure vessel 24. Extraction cartridge assembly 30 may now beopen to empty spent sample.

In FIG. 3, there is shown a simplified perspective view of anotherembodiment 10A of supercritical fluid extraction system having a cabinet400 containing a drive section in its lower portion (not shown in FIG.3), an extraction section in the upper portion of the cabinet (not shownin FIG. 3), a sample injection section 406 and a fraction collectionsection 408. The supercritical liquid extraction system 10A iscontrolled from a panel 410 on the front of the cabinet 400 and thedrive section operates the extraction section, the sample injectionsection 406, and the fraction collection section 408, which cooperatetogether to extract a plurality of samples sequentially and collect theextractant from the samples in separate containers with minimumintervention by an operator.

The liquid extraction system in the embodiment 10A operates in a mannersimilar to that of the embodiment of FIG. 1 but is adapted to cooperatewith the novel sample injector and fraction collector. With thisarrangement, a series of samples to be extracted are preloaded into ameans for holding the samples and the samples are automatically injectedone at a time into the extractor. In the extractor, supercritical fluidis supplied to the samples and an extractant is removed from the samplesone by one. To aid in correlating the embodiment 10 and the embodiment10A, similar parts have the same reference numerals but in theembodiment of FIG. 10A, the numerals include the suffix "A".

The extractant is supplied to individual containers or individualcompartments of one container in a fraction collector. Thus, a pluralityof extractions are performed on a plurality of different preloadedsamples without the need for manually loading samples or initiating theflow of the supercritical fluid for each individual sample. The samplesare automatically mechanically moved one by one into the extractor forextraction instead of being individually physically injected by anoperator.

The cabinet 400 has a lower portion 412 generally shaped as a rightregular parallelopiped with an angled control panel 410 and upstandingupper portion 414 which is another right regular parallelopipedextending upwardly to create a profile substantially shaped as an "L"having a common back portion or rear panel 416 which may contain fansand connections for supplementary pumps and the like. A fluid fitting420 extends from one side to permit near supercritical fluids to beintroduced into the cabinet 400. The L-profiled cabinet 400 has anangled front panel 410 for convenient use of controls and a top surfaceon the foot of the "L" for manipulation of samples to be injected andextractants that are collected.

To permit access to the interior of the cabinet 400, the upper portion414 includes a hinged front access panel 422 having hinges 426 at itstop so that it can be pivoted upwardly. It includes an opening 424 nearits bottom to permit the entrance of fraction collector receptacles thatare relatively tall. It extends downwardly to a point spaced from thetop surface of the lower portion 412 of the cabinet 400 a sufficientdistance to permit the entrance of normal receptacles used in the sampleinjector and the fraction collector.

The sample injection section 406 includes a sample reel 430 which isformed of upper and lower rotatable plates 432 and 434 spaced verticallyfrom each other and containing holes in the upper plate 432 and openingsin the lower plate 434 which receive cylindrical tubular sleeves 436having vertical longitudinal axes and open ends. The upper open end 438permits samples to be received and to be removed as the sample reel 430is rotated into the extractor.

With this arrangement, the sample reel 430 may be rotated to movesamples one by one into the extractor for processing. The sample reel430 is horizontal and extends into the upper portion 414 of the cabinet400 and into the extractor assembly with its vertical center of rotationbeing outside of the upper portion 414 to permit ready access to anumber of the sleeves 436 by users and yet to permit sequential rotationby automatic means into the extractor. In the preferred embodiment,there are 24 sleeves for containing 24 distinctly different sampleswhich can, without human intervention, be moved into the extractor.

To receive extractant, the fraction collection section 408 includes ahorizontal fraction collector reel 440 mounted concentrically with thesample reel 430 but having a smaller diameter to be inside the samplereel 430 having a plurality of openings 442 circularly arranged inspaced apart relationship with each other about the periphery of a topplate 446 of the fraction collector reel 440 and having in its center aknob 444 by which the fraction collector reel 440 may be lifted andremoved from the cabinet 400. With this arrangement, the fractioncollector reel 440 may be lifted and removed or reinserted after thehinged access panel 422 is pivoted upwardly about the hinges 426.

When the fraction collector reel 440 is in place, it is rotatedautomatically through the opening 424 into a location in which one ormore individual containers 442 may receive extractant. The fractioncollector reel 440 is moved alternately with the sample reel 430 andindependently of it so that, after a sample injection and extraction,one or more of the openings 442 are moved into position to receive theextractant prior to the injection of another sample for extraction.

Because the reels 430 and 440 rotate within the upper portion 414 of thecabinet 400 with a portion of its periphery outside of the cabinet 400,the collected extractant may be removed and new sample added duringoperation of the equipment. For this purpose, the receptacles for thefractions and the receptacles for the samples have upward open ends andare mounted with their axes vertical.

In FIG. 4, there is shown a longitudinal sectional view through lines4--4 of FIG. 3 showing the cabinet 400, the drive section 402 within thecabinet 400, the extraction section 404, the sample injection section406 and the fraction collection section 408. The drive section 402includes a control system 450, a sample-and-extractant container reeldrive assembly 452, a sample injector drive 454 and a fluid drive orpump 456. The control system 450 receives information from the controlpanel 410 and conveys information to it through a cable 458. It alsocontrols the pump 456, the sample-and-extractant container reel driveassembly 452 and the sample injector drive 454, which cooperate togetherto move samples into position, inject them into the extractor, pumpfluids through the extractor to extract the samples and collect thesamples in sequence one by one.

To inject samples into the extraction section 404, the sample injectionsection 406 includes the sample-and-extractant container reel driveassembly 452, the sample reel assembly 430, and a cartridge injectorassembly 460. The sample-and-extractant container reel drive assembly452 drives the sample reel assembly 430 to carry a cartridge assembly30A onto the cartridge injector assembly 460 which lifts it under thecontrol of the sample injector drive 454 upwardly into a pressure vessel24A for the purpose of extracting a sample within the cartridge assembly30A. The cartridge assembly 30A and the pressure vessel 24A are similarto the cartridge assembly 30 and pressure vessel 24 of the embodiment ofFIGS. 1-14 and are only adapted such as by having their top and bottomsides reversed to permit the cartridge assembly 30A to be inserted fromthe bottom into the pressure vessel 24A and be more easily sealedtherein for extraction and removed by gravity after extraction.

To drive the sample reel assembly 430, the sample-and-extractantcontainer reel drive assembly 452 includes a central transmission, andmotors on each side that drive the transmission under the control of thecontrol system 450 to drive either one or both the sample injector reelassembly 430 and the fraction collector reel 440.

The sample injector reel assembly 430 includes the top plate 432, thebottom plate 434, both of which are rotatable together to carry aplurality of sleeves 436 sequentially, one at a time, into position forthe repeated injecting of cartridges one by one into the pressure vessel24A and the removal of the cartridges from the pressure vessel 24A andthe return of them to the reel assembly 430 one by one so that only onecartridge is in the pressure vessel 24A at a time.

Within the extraction section 404, a stationary bottom plate 462 has ahole 464, with the hole being aligned with the open-bottom end of thepressure vessel 24A and the upper end of the cartridge injector assembly460. Consequently, the cartridge assemblies such as 30A are rotated oneby one above the open end 464 in the bottom plate 462 for movementupwardly into the pressure vessel assembly 24A by the cartridge injectorassembly 460 under the control of the sample injector drive 454 forextraction of the sample therein. With this arrangement, a stationaryplate 462 holds the cartridge assemblies 30A in place as they arerotated by the upper and lower plates 432 and 434 until they aresequentially brought over the opening 464 through the stationary plate462 for elevation into the pressure vessel 24A.

To inject cartridges into the pressure vessel 24A, the cartridgeinjector assembly 460 includes the sample injector drive 454, a pinion470, a gear 472, a multi-threaded, fast action nut 474, a correspondingscrew 476, and piston or plug 32A. The pinion 470 is mounted to theoutput shaft of the drive gear motor 454 and engages the teeth of gear472. The gear 472 is fastened to or integrally formed with the drive nut474 which, as it rotates, moves the screw 476 upwardly or downwardly.The support platform 475, piston or plug 32A and sample container 30Aare carried by the top of the screw 476 and are moved upwardly anddownwardly. The top surface of the plug 32A, which is supported by thescrew 476 in its lower position is flush with the bottom of the opening464 in the fixed plate 462 to support a cartridge such as 30A thereinand in its top position positions the piston or plug 32A at the bottomof the pressure vessel 24A. Plug 32A carries self-actuated,spring-biased, cylinder seals, such as those made by the Bal-SealCorporation. These seals provide a high pressure fluid-tight sealbetween the plug 32A and the inner wall of the pressure vessel 24A.

With this arrangement, the piston or plug 32A is sealable against thewalls of the pressure vessel 24A during the extraction process aftermoving the cartridge assembly 30A upwardly into the pressure vessel 24A,and after extraction, can move the cartridge assembly 30A downwardlyback to the sample reel assembly 430 for rotation out of the upperinjector housing 414 as a new cartridge is moved into position forinjecting into the pressure vessel 24A. A bearing mount rotatablysupports the nut 474 while maintaining it in the same vertical positionso as to move the rapid-advance screw or other screw 476 upwardly anddownwardly.

The plug 32A serves a function similar to the breech plug 32 in theembodiment of FIGS. 1-14 and contains within it an opening supporting aspring 201A and a support block 482 so that the support block 482 isbiased inwardly against the cartridge end 148A to move the cartridge 30Ainto place against fittings for supercritical fluid.

To extract the sample in the cartridge 30A after it has been moved intoposition and the breech plug 32A fastened in place for a seal,extracting fluid is applied through the fitting 42A in a manner similarto the embodiment of FIG. 1, so that the extracting fluid flows throughone path into the cartridge 30A and through another path over theoutside of the cartridge 30A into the fitting 44A and from there to apurge collector or vent. The extractant, after passing through thecartridge and the sample, exits from a fitting 46A and proceeds to thesample collector in a manner to be described hereinafter.

To pump fluid such as carbon dioxide into the pressure vessel 24A at atemperature proper for supercritical extraction: (1) the pump 456includes a pump head and gear box 490 and an electrical motor 492; and(2) the pressure vessel 24A has an aluminum heating block 22A over it,an opening 278A in the aluminum heating block, a rod-shaped heatingelement 274A in the aperture 278A, the extracting fluid fitting 42A anda heat exchanger 40A entering the aluminum heating block 22A at aperture270A. The motor 492 drives the pump mechanism 490 to pump fluid into theaperture 270A, through the heat exchanger 40A within the aperture 270A,through the connecting tubing 60A and the fitting 42A and into thecartridge 30A and the pressure vessel 24A. The aluminum block 22Acontrols the temperature of the fluid, which may be carbon dioxide orany other useful extracting fluid to keep it above the supercriticaltemperature for that fluid, and for that purpose, the heating rod 274Awithin the aperature 278A is used when necessary to heat the aluminumblock 22A.

The pump 456 may be any suitable pump, but one appropriate pump forcarbon dioxide is a highly modified version of the pump used in the Iscomodel 2350 HPLC Pumping System. sold by Isco, Inc., Lincoln, Nebr.However, for best results when using carbon dioxide, the stroke of thispump is modified from ten millimeters to fifteen millimeters andsmaller, lower trapped-volume check valves are used. These modificationsincrease the compression ratio of the pump from 1.64:1 to 2.64:1 andincrease the displacement by a multiple of 1.5. Additional changes arethe use of: (1) Carpenter Technologies 182FM stainless steel in the pumphead, instead of type 316, for better thermal conducting; (2)differently shaped cam; and (3) heavier bearings.

To collect extractants, the fraction collector section 408 includes thefraction collection reel 440, the sample-and-extractant container reeldrive assembly 452, a purge fluid outlet system 520 and an extractantfluid outlet system 522. The fraction collection reel 440 movesreceptacles such as 98A into position within the housing 414 where theextractant fluid outlet system, 522 to be described in greater detailhereinafter, causes fluid from the fitting 46A in the pressure vessel24A to flow outwardly and into the receptacle 98A after piercing a sealtherein. The purge fluid system 520 causes purge fluid to flow from thepurge fluid fitting 44A to a pressure control unit and finally to anexhaust or collection unit.

To move the collection receptacles 98A into position, the fractioncollection reel 440 includes a knob 444, an intermediate plate 448, anupper plate 446, a lower disk plate 530 and a drive rod 532. The driverod 532 rotates within the fixed disk 530 and carries above them theupper and lower plates 446 and 448. The upper and lower plates 446 and448 have aligned circumferentially spaced holes through them, each ofwhich can receive a collection vial such as 98A. The lower disk 530 doesnot have holes and supports the plates as they are moved. The knob 444may be used to lift the fraction collector reel 440 from the center ofthe sample injector reel 430 after the hinged front access panel 422 hasbeen opened about its hinge 426.

The sample-and-extractant container reel drive assembly 452 moves thecollection vials one by one inside the upper portion of the housing 414to receive extractant. One or more such vessels 98A may be moved inplace each time a sample cartridge 30A is extracted so that thereceptacles 98A are moved alternatively with the sample cartridges 30A,although several receptacles 98A may be moved in the time between movingone of the sample cartridges 30A into a pressure vessel 24A and the timethe sample cartridge is removed from the pressure vessel 24A.

In operation, the extractant passes through fitting 46A and into thefraction collector receptacles 98A in a manner to be describedhereinafter. The purge fitting 44A communicates with the extractionvolume in the cartridge 30A and is connected to a Tee-joint tube, 542through tubing 62A. A second arm of the Tee-joint tube 542 is connectedto an over-pressure safety diaphram 540 calibrated to burst at 15,000pounds per square inch. This is an excess of the maximum rated workingpressure of 10,000 pounds per square inch for pressure vessel 24A. Theremaining arm of the Tee-joint tube 542 is connected to the purge valve52A. The other side of the purge valve 52A is connected to the firstside of a second Tee-joint tube 544 through the tube 64A. The secondside of the Tee-joint tube 544 is connected to an exterior vent port 546through a tube 548. The third arm of the Tee-joint tube 544 is connectedto the exhaust tube 110A which vents the fraction collection vial 98A.With this arrangement, the purge fluid flowing through fitting 44A isremoved and a tube connected to the vent port 546 is also used to ventthe sample receptacle 98A in a manner to be described hereinafter.

In FIG. 5, there is shown a simplified sectional elevational view of theembodiment 10A of supercritical fluid extractor taken through lines 5--5of FIG. 4 having the sample-and-extractant container reel drive assembly452, the pump 456 and the extractant fluid outlet system 522. Thesample-and-extractant container reel drive assembly 452 may selectivelymove either the sample reel 430 or the fraction collection reel 440under the control of the controller 450 (FIG. 4).

To selectively drive the fraction collection reel 440, thesample-and-extractant container reel drive assembly 452 includes afraction collection spindle 532, a tubular shaft 580, a bevel gear 582,a bevel gear 584 and a gear motor 586. The controller 450 controls thegear motor 586 to rotate the fraction collection reel 440. For thispurpose, the spindle 532 is held by the tubular shaft 580. The bevelgear 582 is fastened at the end of the spindle 532 and meshes with thebevel gear 584 on gear motor 586. The controller 450 causes the motor586 to rotate its output shaft so as to drive the collection reel 440(FIGS. 15 and 16) and not the sample injector reel 430 (FIGS. 3 and 4).

To move the sample injector reel 430, the sample-and-extractantcontainer reel drive assembly 452 includes the tubular shaft 580supported by bearing block 590, fraction collection spindle 532, bevelgear 588, bevel gear 592 and gear motor 594. The controller 450 actuatesgear motor 594 to cause the bevel gear 592 to rotate. The bevel gear 592meshes with the bevel gear 588 which is attached to the bottom end ofthe fraction collection spindle 532.

To cause extractant to flow into the fraction collection vial 98A, theextractant fluid outlet system 522 includes a gear motor 552, a pinion554, a gear 556, a lead screw 558, an arm 560, and a restrictor tube66A. The vials 98A have a seal 550 over the top, which seal can bepierced.

To cause the seal 550 to be pierced and extractant to flow into the vial98A, the controller 450 starts the gear motor 552 which rotates itspinion 554 which is in engagement with the gear 556. The pinion 554rotates the gear 556, which engages and is fastened to the rotating leadscrew 558. The arm 560 is mounted for movement by the lead screw 558 andlowers it into a position where the restrictor tube 66A pierces the cap550 on the collection vial 98A, and moves its tip below the surface 564of the collection fluid within the vial 98A. As the extractant flowsinto the tube, exhaust is removed from the tube through an exhaust tube110A (FIG. 4 in addition to FIG. 5).

If either the tube 66A or the tube 110A are stiff or otherwiseinconvenient to bend, it is advantageous to raise the collecting vial98A up to tubes 66A and 110A, instead of lowering the tubes into thecollecting vial. This alternate arrangement does not pose any difficultyas the collecting vial 98A may be raised by a support similar to plug32A, which support is connected directly to plug 32A so that it movessynchronously with plug 32A.

With either arrangement, extractant flows through the fitting 46A (FIG.4) from the sample cartridge 30A (FIG. 4) through the tubing 522 (FIG.4), the valve 50A and the restrictor tube 66A. Extractant residing inbubbles from the tube are captured through trapping fluid 104A wherebyextractant is trapped in the trapping fluid 104 in the vial 98A andextracting fluid passes out through the exhaust tube 110A, Tee-jointtube 544 (FIG. 4), tube 66A and exhaust port 546 (FIG. 4). Aftercollection of the extractant, the motor 552 moves in the reversedirection and raises arm 560 which removes the restrictor tube 66A andexhaust tube 110A from the vial 98A.

Because the pump head 490 is heated by pumping at high compression, boththe pump head 490 and incoming fluid line are preferably cooled. In thepreferred embodiment, they are cooled thermoelectrically (Peltiereffect). The pump head 490, the inlet check valve housing 494 are formedof Carpenter 182FM stainless steel rather than type 316 stainless steelto increase their thermal conductivity.

In pumping, the pump drive motor 492 (FIG. 4) drives a cam within camhousing 495 through appropriate gear train within the gear housing 496.The rotating cam within the cam housing 495 operates a pump plungerwhich cooperates with the pump head 490A (FIG. 5) to draw liquid carbondioxide through inlet check valve assembly 494 and discharge it throughoutlet check valve assembly 436. In one embodiment, the Peltier coolingplate 500 is mounted to the flat face of the pump head 490A (FIG. 5)with cooling fins 502 mounted for good thermal contact to the oppositeside of the Peltier cooling plate 500.

When an electric current is passed in the proper direction through thePeltier cooling plate 500, heat is withdrawn from the pump head 490A(FIG. 5) and rejected into the cooling fins 502. A fan 504 driven by anelectric motor 493 (FIG. 5) withdraws heat from the fins 502. AnotherPeltier-effect cooled heat exchanger is also utilized in the inlet line.

To control the speed of the motor 492 (FIG. 4), a tachometer wheel 505is mounted to the shaft of motor 492 (FIG. 4) with a photoelectrictachometer sensor 510 mounted to provide signals reading indicia on thewheel. The signals from the photoelectric tachometer 510 indicate thespeed of motor 492 and thus the pumping speed of pump 456. These signalsare compared in the controller 450 and utilized to control the speed ofthe motor 492.

To control the pressure on the outlet line 512 from the pump, a pressuretransducer 514 (FIG. 6) generates a signal indicating the pressure. Thissignal is used as a feedback signal to control the pumping speed. Thisstructure is provided by existing pumps such as the Isco model 260Dpump.

In FIG. 6, there is shown a sectional view, partly simplified, takenthrough lines 6--6 of FIG. 4 having a locking mechanism 614 for lockingplug 32A into the pressure vessel 24A and a control mechanism 616 forcontrolling the extraction fluid. As best shown in this view, thelocking mechanism 614 includes a gear motor 600, a pinion 602, a rack604, a locking pin 606, a hole 609 in the pressure vessel 24A and a hole610 in the piston or end piece or breach plug 32A and a hole 612 throughthe other side of the pressure vessel 24A. Instead of a pin 606, a yokeof the type conventionally used as a Winchester 94 rifle lockingmechanism advantageously may be used. This type of locking mechanism isa yoke mounted to a pinion 602 and rack 604 as shown in FIG. 6. In thismechanism, a plate with a slot cut out of it to form a yoke is moved bythe rack and pinion to pass under the plug 32A to hold it againstpressure and provide strong support therewith by further engaging slotsin the pressure vessel 24A. The aforementioned slot in the plateprovides clearance for the screw 476.

In operation, the gear motor 600 is caused by the control system 450(FIG. 4) to drive locking pin 606 through the opening 609 in thepressure vessel 24A, through the opening 610 in the piston 32A andthrough the opening 612 in the pressure vessel 24A by rotating thepinion 602 to drive the rack 604 that carries the locking pin 606, thuslocking the cartridge 30A (FIG. 4) in place within the pressure vessel24A.

To control the flow of extracting fluid from the pump 12 (FIG. 1) intothe pressure vessel 24A and cartridge 30A, the control mechanism forextracting fluid includes the gear motor 570 and valve 54A that isconnected at one end to the conduit 58A that extends from line 512 andpressure transducer 514 to the conduit 58 which passes into the heatexchanger 40 (FIG. 1). In operation, the gear motor 570 under thecontrol of the control system 450 opens the valve 54A to permit the flowof extracting fluid into the cartridge 36A and pressure vessel 24Aduring an extraction operation. It also rotates in the oppositedirection after extraction is complete to close the valve 54A.

The sample cartridge 30A (FIG. 4) is composed of a tubular sleeve orbody portion 140A (FIG. 4) and end pieces 144AA (FIG. 4) and 464A (FIG.4). The end pieces 144A and 464A are made of stainless steel or an inertplastic and carry a stainless steel frit or filter disk centered in theinterior of each. The flat, narrowed ends of the tubular sleeve 140Aseal against PTFE washers around the frits which seal against the endpieces at the location between the diameters of the filter disks and theinside diameters of the end pieces 144A or 464A respectively. In FIG. 7,there is shown a cooled pumping unit having a cylindrical pumphead block300, a piston drive assembly 302, a piston 304, a chamber 336, a coolingassembly 306, and a heat exchanger 763 for transfering heat from thepumphead block 300 to the cooling assembly 306, connected together topump fluid while cooling the fluid and pump with air-thermoelectriccooling. The heat exchanger 762 (FIG. 10) for transferring heat from thefluid into the cooling assembly is not shown in FIG. 7 but is shown inFIGS. 10 and 11. Fluid volume is measured by pressure and movement ofthe piston 304 within the chamber 336. The cooling assembly 306 and theheat exchangers 762 and 763 (heat exchanger 762 not shown in FIG. 7) donot use liquid cooling but the pumping system is cooled entirely by airand not by a liquid coolant.

The cylindrical pumphead block 300 includes threaded recesses forreceiving a generally cylindrical fluid outlet check valve 308 and fluidinlet valve 310. The fluid outlet check valve 308 incorporates: (1) athreaded recess 312 for a conventional fluid coupling fitting; (2) ballcheck valve elements 314 and 316; (3) valve seats 318 and 319; (4) thecylindrical passageway 330. The cylindrical passageway 330 communicatesbetween the check valve element 314 and the pumping chamber 336 andcontains fluid in contact with the fluid in the pumping chamber 336. Thevalve elements 314 and 316 cooperate with valve seats 318 and 319respectively in a manner known in the art to form a conventionaldual-ball check valve assembly that blocks the flow of liquid into thechamber 336 and permits flow from the chamber 336 to the pump outlet.

The fluid inlet valve 310 incorporates: (1) a threaded recess 320 forreceiving a conventional fluid coupling fitting; (2) check valve ballelements 322 and 324; (3) valve seats 326 and 328; and (4) thecylindrical passageway 334. The check valve ball elements 322 and 324cooperate with valve seats 326 and 328 in a manner known in the art toform a conventional dual-ball check valve assembly controlling the flowof liquid into the chamber 336 and blocking flow of fluid from thechamber 336. The cylindrical passageway 334 communicates between thecheck valve element 322 and the pumping chamber 336 and contains fluidin contact with the fluid in the pumping chamber 336.

To limit the trapped fluid volume in the pumphead, the diameter of thefluid passageways 330 and 334, the annular volume between the piston 336and the bore 370, and the interval volume of the seal 356 aresufficiently small to restrict the trapped liquid to no more than 0.9times the displacement and to restrict the compression ratio to no lessthan 2.1:1. In the preferred embodiment, the passage 334 is only onemillimeter in diameter and the passage 330 is even somewhat smaller. Ahigh compression ratio (ratio of volume before compression to volumeafter compression by the pump) is especially advantagous for pumpingvery compressible liquids such as liquid carbon dioxide because the highcompression ratio tends to quickly discharge the compression-heatedfluid before it heats the pump head 300 and also improves the volumetricefficiency which is otherwise degraded by compression of the fluidduring the compression/delivery stroke. Volumetric efficiency is definedby the amount pumped per stroke divided by the displacement. Highervolumetric efficiency results in a higher maximum flow rate. Compressionratio is less important to HPLC pumps because of the lower compressionratio and have a reason for needing larger inlet fluid passageways. HPLCpumps must have larger inlet fluid passageways because of cavitationproblems.

The check valve balls 314, 316, 322 and 324 are preferably spheres madeof synthetic ruby and the valve seats 318, 319, 326 and 328 are made ofsynthetic sapphire. The pumphead block 300 is made of stainless steel,preferably Carpenter type 182FM stainless steel because of itsrelatively high thermal conductivity (for a stainless steel), its goodcorrosion resistance and ease of machineability. In those cases wherethe requirement of ease of machineability is low, half-hard nickle maybe used because of the superior thermal conductivity of half-hardnickle.

To move the piston rod 304, the piston drive assembly 302 includes adrive cam 338, a roller cam follower 342, a ferrule-anvil combination352 and 350, a compression spring 384, a yoke 346 and a tubular slide348 as its principal parts. The ferrule is attached by injection-moldingonto the right end of the synthetic sapphire displacement rod, or pistonrod 304. The yoke 346 is an integral part of the tubular slide 348 whichsupports the anvil 350. A circumferential groove 358 ground into thepiston rod 304 insures a firm mechanical coupling between ferrule 352and rod 304. The ferrule 352 is made of the same material as the anvil350. Alternatively, the anvil can be made of polished stainless steel.The former material is a low coefficient friction plastic havingrelatively high compressive strength and relatively low compressivemodulus. It is injection molded to form the ferrule 352 and the anvil350. The ferrule 352 is molded onto the rod 304.

The drive cam 338 drives the cam follower 342, which in turn drives theferrule 352 downwardly against the pressure of the compression spring384. The rod or plunger 304 moves with the ferrule 352 to reciprocate inthe chamber 336 to pump fluid through the outlet valve 308. The rollercam follower 342 is mounted to rotate on a trunnion 344 mounted in theyoke 346 mounted to the anvil 350 for rotation therewith.

The reciprocating sapphire piston rod 304 is shown in its maximumretracted position in FIG. 7. Rotation of drive cam 338 in the directionindicated by the arrow 341 forces the roller cam follower 342 mounted ontrunnion 344 to move the yoke 346 in a direction that expells fluidwhich in the preferred embodiment is toward the inlet and outlet shownto the left in FIG. 7.

To improve piston seal life, the surface of the ferrule 352 that isengaged by the anvil 350 during a piston stroke is a spherical surfacehaving a radius large enough so that, in case of misalignment withrespect to anvil 350, the line of contact and direction of force betweenthe spherical surface and the anvil does not have a significantly largecomponent perpendicular to the axis of the piston rod 304. With thisarrangement, the piston 304 is not forced out of alignment during apiston stroke. This reduces wear in the tubular bearing 354 and the seal356 and prevents the rod 304 from breaking.

To reduce wear on the bearing 354, anvil 350 and ferrule 352 are inhertzian contact with each other. With this arrangement, the amount ofdepression of the spherical surface of the ferrule 352 and the forceslateral to the radius of the spherical surface that is normal to theanvil 350 is related to the compressive modulus of the ferrule material,the diameter of the spherical surface and the normal force. Therelatively high strength of the material used, General Electric bearinggrade polyetherimide resin "Ultem 4001", of 21,200 psi compressivestrength and relatively low compressive modulus of 450,000 psi, producesa hertzian force at maximum operating pressure of only half of thecompressive yield strength of ferrule 352 and anvil 350.

Because most conventional materials for such uses, such as for example,hardened type 440C stainless steel, tend to stress-corrode and becauseof the high compressive modulus of that material, the hertzian contactforces in this embodiment are sufficient to make them unsatisfactory forthe purpose. However, the much softer Ultem #4001 used in the preferredembodiment is paradoxically satisfactory.

Unlike most pumps used for other purposes, the inlet fluid is underpressure that forces it into the pump chamber 356. There is a narrowclearance between the piston 304 and the walls 370 of the pumpingchamber so the piston does not quite touch the walls 370. Instead, thepiston rod 304 fits within and is principally guided by a first bearingsleeve 364. The sleeve 364 is force-fit into cylindrical recess 366formed within the pumphead 300 with a larger diameter than the diameterof the pump chamber 336 and joining the walls 370 of the pump chamber336 at a shoulder. The inside diameter (walls 370) of the pump chamber336 is slightly larger than the inside diameter 368 of sleeve 364 sopiston 304 does not come in contact with the inside diameter of chamber336.

The internal diameter 368 of first sleeve 364 is an almost-snug, slipfit with respect to piston 304. The diametrical clearance is only about0.001 inch and therefore, the sleeve acts as a linear bearing whichclosely and accurately guides the reciprocating motion of piston 304.Helical-toroidal spring-loaded self acting seal 356 is located in thehole 372 bored in pumphead block 300. The spring in the spring-loadedseal 356 improves the reliability of the seal. The seal used is aBal-Seal type #X41641. The seal is backed up by ring 374 made ofunmodified polyetheretherketone.

The bearing sleeve 364 is preferably made of a material softer than thatof stainless steel pumphead 300. It should have a suitable spectrum ofchemical resistance, a low coefficient of friction against piston 304and should be dimensionally stable. It is believed that the suitablebearing materials should have a yield strength between 5,000 to 20,000psi and adequate deformability.

Suitable materials if the pump is not intended to be used to pump fluidscontaining acid in the presence of water are No. 1 babbitt (tin with4.5% copper and 4.5% antimony), or an alloy of tin containing 10% goldfor hardening and increased corrosion resistance. The latter alloy has acorrosion resistance which is about twice as good as that of No. 1babbitt. No. 1 babbitt, in turn, has corrosion resistance superior tothat of any of the other babbitts.

Neither of these materials have corrosion resistance as good as thestainless steel pumphead block 300. Soft-metal bearing materials whichhave at least as good a corrosion resistance as the other wetted metalswithin the pump are gold or pure palladium annealed to a yield strengthon the order of 6,000 to 10,000 psi. The materials for the bearingsleeve 364 either do not have an extremely broad spectrum of corrosionresistance (the tin alloys) or they are expensive (the precious metals;however palladium is not excessively expensive). Accordingly, thespecific material is selected as trade-off between cost, the use of abearing sleeve of a soft metallic material and corrosion resistancedepending on the intended use of the pump.

Metals generally have high thermal conductivities and it is desirable toefficiently remove the heat of compression of a compressible fluid beingpumped at a temperature close to its supercritical temperature. Ifsufficient heat of compression is not removed; the fluid gets too warm,its density drops rapidly and its compressibility increases rapidly,making it difficult or impossible to produce a reasonable mass flow withthe pump.

To permit adequate heat removal from the fluid with a preferred materialfor the piston and the sleeve, the metallic wall 370 is in contact withabout half the maximum volume of fluid within the pumping chamber 336and serves on its own for a significant amount of heat removal withinthe pump chamber. Therefore, it is possible to use a low thermalconductivity material for the bearing sleeve 364 with a moderatedegradation of performance. Suggested non-metallic materials for thissleeve include DuPont "PFA" perfluorinated polyether plastic or, ICI"PEEK" plastic. These materials swell a small but significant amount inliquid carbon dioxide at high pressure, so a sleeve made of one of thesematerials must be originally machined to a greater diametrical clearancethan the 0.001 inch used for a metal sleeve.

The pumphead block 300 is nutted tightly onto type 303 stainless steelstuds 715 and 717 (FIG. 12) through support block 376 and into 203EZ(Ryerson) stainless steel guide sleeve 378. Support block 376 isinjection molded from ICI type 450CA30 PEEK (carbon fiber reinforcedpolyetheretherketone). The 303 stainless studs are not shown since theyare out of the plane of the section shown in FIG. 7. They are indicatedas 715 and 717 in FIG. 12. Their nuts are recessed into pumphead 300.The support block 376 has relatively low thermal conductivity andthermally insulates the pumphead block 300 from the support sleeve 378.A recess 380 within support block 376 loosely supports tubular bearing354 in the diametrical direction. Bearing 354 is preferably made of alow friction, strong plastic such as ICI type 450CF30 grade of PEEK. Thebottom of recess 380 is in light face-to-face contact with the right endof tubular bearing 354, which tightly compresses it against backup disk374 when the type 303 stainless mounting bolts (FIG. 12) are tightenedduring assembly.

In operation, as the cam 338 rotates on shaft 382, the sapphire piston304 is urged to the left until it reaches its maximum leftward excursionwith its end fairly close to the left end of the pumping chamber 336.The cam 338 continues to rotate past the maximum and then compressionspring 384 and pressure within the chamber 336 urge piston 304 to theright with needle-bearing roller cam follower 342 remaining in contactwith the periphery of the cam 338.

This reciprocating motion of the piston rod 304 continues and provides apumping action for fluid entering the inlet fitting at 320 and exitingthe fitting at 312 in the manner usual with reciprocating fluid pumps.The diameter of the piston 304 is 1/8 inch and its longitudinal motionduring one rotation of cam 338 is 15 millimeters. This results in adisplacement of 0.12 milliliter per stroke of the plunger 304.

Because of the heat of compression of liquid carbon dioxide, there mustbe some arrangement for removal of heat, or the temperature of liquid inthe pumphead 300 will correspond to a vapor pressure higher than thesupply pressure feeding the inlet valve 310 of the pump. Under thiscircumstance, the pump neither fills nor delivers fluid. Some prior artarrangements overpressurize the CO₂ supply tank with helium to solvethis problem. This has several disadvantages, such as: (1) the heliumoverpressure in the headspace above the liquid CO₂ decreases as the tankempties and the headspace volume increases; (2) the helium dissolvesinto the liquid CO₂, decreasing its density which decreases its qualityas a supercritical fluid extraction solvent; and (3) CO₂ from tanksincorporating helium pressurized headspace is more expensive than thatfrom tanks filled with CO₂ alone.

To permit carbon dioxide to be pumped without helium overpressure, thecooling assembly 306 and the heat exchanger 763 in the preferredembodiment incorporates thermoelectric cooling element 386 which removesheat from aluminum heat coupling spreader plate 390 which in turn is inclose thermal contact with pumphead block 300. Melcor type CP1.0-127-05Lthermoelectric elements and Melcor type CP1.4-127-045L thermoelectricelements provide satisfactory results, with pelcor type CP1.4-127-045Lproducing the better results of the two elements. The heat couplingspreader plate 390 is desirable since the thermoelectric element 386 issquare and its corners would protrude past the outside diameter ofpumphead block 300. The heat rejected from pumphead 300 and spreadingplate 390 to the thermoelectric cooling element 386, plus the electricresistive heat generated within the cooling element 386 is connected tofinned aluminum extrusion 392 which provides for heat removal. The heatremoval extrusion 392 is surrounded sheet metal shroud 394 definingmultiple cooling air passages such as 396 for forced air cooling to bedescribed later. No liquid cooling is used in any form.

Stepped screws 398 and 401 thread into the pumphead block 300 atlocations 711 and 713. The steps of the screws force heat spreader plate390 against the pumphead 300. The stepped screws respectively have handknobs 403 and 405 and compression wave washers 717 and 715 which forceshroud 394 of cooling assembly 306 to the right, pressing finnedaluminum extrusion 392 into good thermal contact with thermoelectricelement 386.

The cooling assembly 306 may be removed from the pumphead 300 byunscrewing screws 398 and 401 with knobs 403 and 405, releasing theshroud 394 and fins 392, also releasing thermoelectric element 386 andheat spreader plate 390, which have been sandwiched between the finnedextrusion 392 and pumphead 300. This provides access to the twostainless steel screws 715 and 717 (FIG. 12), the heads of which arerecessed into pumphead block 300. These screws hold the pumphead to thespacer block 376 to the mounting sleeve 378. The removal of these screwsprovides for removal of pumphead block 300 so that seal 356 can bereplaced if necessary.

Removal of cooling assembly 306 and heat exchanger 763 adds to thedifficulty of getting access to seal 356 for its replacement. Tocompensate for this, it is desirable to increase the life of the seal sothat replacement is less frequent. To this end, bearing sleeve 364 keepsthe piston 304 centered very accurately within the center of seal 356,thus prolonging the life of the seal far past what is usual with thistype of pump. This collinearity minimizes the radial stress on the sealand provides a remarkably longer seal life.

To insure that the center lines of sleeve bearing 364 and seal 356follow the same line, the following three steps are initially taken inmanufacturing the pumphead 300, which three steps are: (1) the bores 370and 366 are made in pumphead block 300; (2) a solid rod of the materialselected for the bearing sleeve 364 is turned to an outside diameterwhich forms a good force fit in bore 366; and (3) the sleeve 364 is thenforce fitted into bore 366.

After the sleeve 364 is force fitted into bore 366, the following twosteps are taken, which are: (1) the pumphead block 300 is chucked in anaccurate lathe and the recess or gland 366 for seal 356 is turned; and(2) without disturbing the lathe setup any more than is necessary tocarefully change boring tools, the inside bore 368 of bearing sleeve 364is bored, leaving the center of gland 366 and the center of bore 368 ofsleeve 364 collinear.

After removal from the lathe, the following three steps are taken, whichare: (1) if palladium is used for the bearing sleeve 364, the pumpheadblock 300 and the sleeve 364 are annealed at 820 degrees centigrade forfive hours in a low pressure argon atmosphere and cooled in theatmosphere; (2) the cool pumphead block is removed from the heattreating furnace, the seal 356 is assembled into gland 366 and thebackup disk 374 is assembled outside of it; and (3) before the pumpheadblock 300 is assembled onto bearing 354, which in turn floats radiallywithin backup block 376, and within mounting sleeve 378, the cam 338 isrotated so that piston 304 is retracted until it does not protrude tothe left much farther than shown in FIG. 7.

To permit rotation of the plunger 304 so that it is retracted, opticalflag 722 (FIG. 12) and sensor 724 (FIG. 12) in cooperation with the pumpcontroller, provide push-button capability for the user to operate themotor drive to rotate the cam 338 under program or computer control to aposition that moves the piston 304 only so far out that it will fillabout half or a third of the length of sleeve 364 when the pumpheadblock 300 is assembled onto support block 376 and guide sleeve 378. Itis undesirable at this time for the plunger 304 to move further out, asthis unnecessarily subjects it to increased chance of breakage when thepumphead is put onto the plunger.

Next, when the pumphead block 300 is inserted onto the rod or piston304, the piston 304 becomes accurately constrained into position by theinside surface of bearing sleeve 364 well before backup ring 374 startsto compress and locate against radially floating bearing sleeve 354 whenthe pumphead block 300 is slid on over holding studs (FIG. 12), whichare nutted and tightened. As a result, bearing sleeve 354 is collinearlylocated with respect to rod 304 and sleeve 364 before such compression.

After this compression, second bearing sleeve 354 becomes radiallylocated and locked in place by compressive forces, such that its centeraxis is collinear with the center axes of first bearing sleeve 364 androd 304. This leaves the piston 304 being constrained to reciprocatewith its center axis collinear with the center axis of seal 356 sincefirst sleeve 364 is collinear with the seal. The rod 304 is supported onboth sides of the seal 356 by first and second bearing sleeves 364 and354. The axis of rod 304, the axis of the bore in first sleeve 364, theaxis of the seal 356 and the axis of the bore of second sleeve 354 areall collinear with respect to each other. The resulting accurate androbust collinear alignment of rod 304 with respect to seal 356 providessubstantially and reliably increased seal life and there is negligiblesidewise or misalignment wear of the seal.

The piston rod 304 is constrained to operate with close collinearitywith the center axis of the pump chamber 336 since the bearing sleeve364 is immediately adjacent and in the same block of metal. Thus, thepump chamber wall 370 of chamber 336 does not need to have an internaldiameter which is much greater than the diameter of the piston 304,decreasing the unswept volume in the pumphead. It increases thecompression ratio to 2.64 to 1, an amount which compares well to anembodiment wherein the spring in the seal 356 of this application isreplaced with a solid plastic ring. The resulting high compression ratiois needed to provide the high volumetric efficiency required for highflow rate capability when pumping very compressible liquids to a highpressure.

Because the seal, sleeve bearing and plunger are located or imbeddedwithin the pumphead rather than being located behind the pumphead as insome other pumps, there is no risk of the plunger running into the wallsof the pumping chamber such as in the vicinity of the fluid passages 330and 334 leading to the check valves and becomming chipped if thediameter 370 of the pump chamber is made small enough to obtain a goodcompression ratio. If the plunger were to become chipped, the plunger orthe chips themselves could then destroy the seal, thus defeating theeffort to prolong seal life by providing coaxiality of the plunger withrespect to the seal.

To maximize the speed of repressurization and refill of the pump chamber336 without increasing the peak torque seen by the mechanical parts ofthe pumping system, the maximum reverse torque due to depressurizationof the fluid in the pump chamber 336 (FIG. 1), as seen by the motor 726(FIG. 12) or the cam shaft 382 is made substantially equal to themaximum torque during delivery at maximum pressure. This minimizesoperating noise and maximizes reliability. This is an important factorfor pumps which pump prepressurized and compressible liquid, as is thecase with pumps which pump liquids near their critical points, and alsogenerally as pumps for supercritical fluid supply. It is importantbecause of the high stored energy of compression which is not the casewith high performance liquid chromatography pumps.

In FIGS. 8 and 9, there are shown two versions 730 of the cam 338 andtwo versions 728 of the cam-operated plunger displacement curve 736. Thetwo version of the cam 338 shown at 730 differ from each other by theportions of the outline 732 and 734. The version with the shape shown at732 is identical to the cam 338 in FIG. 7. The version with shape 734has a shape similar to a conventional fast-refill HPLC pump cam.

In FIG. 9, there is shown a development or cam follower displacementprofile 736 for a 0.75 inch cam follower indicating linear movement ofcam follower 342 (FIG. 7) and piston 304 (FIG. 7) corresponding to onerevolution of the cam. A 0.875 inch diameter cam follower has longerlife and the difference in displacement profile is negligible. Acomparison of the displacement profile of a HPLC cam with the cam 338 isshown at 728. The curve labeled 738 corresponds to cam surface 732 ofcam 338 in FIG. 7 and the curve labeled 740 corresponds to aconventional fast-refill HPLC pump cam; cam surface 734 of cam 338. TheHPLC-style cam (curve 740) produces a peak reverse torque of about twicethe delivery torque at a pressure of 7500 psi. The cam 338 representedby development 738 produces a peak reverse torque equal to that of thedelivery torque. This is accomplished without decreasing the time of theforward stroke (delivery direction) or increasing the time of thereverse stroke (i.e. depressurization and refill).

With this arrangement, the maximum delivery torque is not increased anddelivery pressure pulsations are unchanged. This, of course, does nothappen without foregoing certain characteristics of HPLC pump cams, suchas for example: gentle refill followed by a wait (nearly zero camfollower velocity) region for the pump chamber to fill and the inletcheck valves to close. This is necessary for HPLC pump cams to avoidcavitation. It is not necessary for supercritical fluid extractionsupply pumps because the supply liquid pressure corresponds to roomtemperature vapor pressure and the liquid vapor pressure in the pumpingchamber corresponds to a temperature about 10° C. lower.

Position A on the cam 338 (FIGS. 7 and 8) represents maximum radius ofthe cam or the top dead center (extended) position of piston 304. Thepoint on the cam at which depressurization ends and refill of the pumpchamber 336 starts is indicated as position C. The minimum radius of thecam is indicated as position E and corresponds to maximum volume in thepumping chamber 336 and maximum withdrawal of the piston 304. PositionsA, C, D and E respectively correspond to rotational positions of cam 338such that positions A, C, D and E are in contact with cam follower 342and also relate to the corresponding position on the cam development 736so that position E' occurs every 360 degrees of rotation, as bettershown in the development 736 (FIG. 9) between E' and E. Starting atposition E', a first part of surface E'-A is the repressurizationsurface. The remaining (second) part of surface E'-A is the deliverysurface. The surface near and on each side, of position A is thetransition surface. Surface A-C is the depressurization surface andsurface C-E is the refill surface.

Reverse torque reflected on the cam 338 by cam follower 342 iscontrolled to a value nearly equal to the delivery torque at campositions extending from position A to position C. The starting slope ofdisplacement after top dead center velocity of the cam follower 342 andtherefore the piston 304 (after position A) should be equal and oppositeto the displacement slope produced by the linear spiral contour of thecam before top dead center of the cam (before position A). The deliverysurface displacement slope decreases to zero as it approaches positionA. The displacement slope of the depressurization surface is zero atposition A and then its magnitude increases to the negative of thedelivery displacement slope. The resulting rounded area, the transitionsurface about position A, decreases Hertzian contact forces with the camfollower to prevent deformation of the cam, excess motion of the camfollower and allows the outlet check valve 308 (FIG. 7) to shut gentlywithout damage because the velocity of the piston 304 and the velocityof the pumped fluid is low.

The displacement after top dead center is a function of cam rotation andshould increase in an accelerating manner until position C. Position Ccorresponds to depressurization of the pump chamber to the supplypressure. In the case of carbon dioxide with a supply pressure of 870psi, a fluid temperature of 15 degrees C. and a head pressure of 7500psi, the compression is about 1.25. This corresponds to an increase inpump chamber volume of 1.25× the dead volume.

The displacement rate or plunger velocity with respect to cam rotationshould accelerate continuously as cam rotation increases from position Ato position C. Torque on the cam shaft is proportional to thedisplacement slope times the pressure on the piston 304. Therefore,torque on the cam shaft from position A to position C is kept constantif the slope of the displacement is proportional to the reciprocal ofthe pressure on the piston 304.

The pump chamber refills with supply liquid between positions C and E.During this period, it is desirable that the acceleration be small(nearly constant displacement velocity) as this is an efficientcondition for receiving supply fluid with minimal pressure drop andminimal chance of vaporization. Such a relatively linear region isgenerally indicated as position D. For smooth running, it is desirablethat there not be a discontinuity of slopes between the join ofdepressurization A-C and the refill surface C-E. By measurement of motorcurrent, it has been discovered that pumps operating at constantrotational speed and incorporating this feature produce adepressurization torque (and also a refill torque) of the same magnitudeas the delivery torque.

In one embodiment, the cam and the electric drive motor are permitted topassively overspeed during the reverse-torque interval ofdepressurization and refill of the pump chamber. This provides: (1)small but beneficial increase in the maximum pumping rate at highdelivery pressures; and (2) simplifies the circuitry for the motor drivebecause the motor speed does not have to be controlled under reversetorque conditions. The servo loop is used to control the motor speedduring fluid delivery and operates similarly to that disclosed in U.S.patent application Ser. No. 07/843,624; now U.S. Pat. No. 5,360,320,MULTIPLE SOLVENT DELIVERY SYSTEM, Daniel G. Jameson, et al. A motordrive system, may be used in which each stroke of the reciprocating pumpis controlled in a manner analogous to that of each stroke of a syringepump in U.S. Pat. No. 5,360,320. The major difference is that it hasbeen found advantageous to combine the instantaneous pressure duringdelivery of a present pump stroke with the average or integratedpressure throughout the delivery of the previous pump stroke and to usethis pressure information for pressure feed back purposes. Using thiscombined pressure feedback signal for motor control produces a morestable and accurate control system.

On a typical HPLC pump cam, the displacement curve just after position Ahas a shorter (usually less than half) radius of curvature than thedisplacement curve just before position E. The displacement curve afterposition A has a short radius to quickly traverse throughdepressurization and start the refill quickly so that the time for therefill period is relatively long and gentle. Gentle refill is necessaryto prevent cavitation in the pump chamber as the incoming fluid is onlyat atmospheric pressure so the onset of cavitation inside the pumpheadmay be at a pressure of only 10 psi less than atmospheric. This pressuredrop can readily be exceeded due to viscous and inertial fluid forces inthe inlet valve and inlet line if the inlet stroke is too violent.Cavitation causes an unreliable or varying flow.

However, the pumping system 12 is supplied with a high pressure liquidsuch as carbon dioxide at 22° C., which is pressurized by its own vaporpressure of about 870 psi and thus is less susceptible to cavitation.The pump is cooled below 16° C., which reflects a vapor pressure that isat least 100 psi lower. This is about 10 times the suction pressureavailable to an HPLC pump.

At the end of the inlet period, the cam of a typical HPLC pump causes agentle (large radius of curvature of displacement) deceleration and alengthy dwell at nearly zero velocity to allow time for the inlet checkvalve 310 (FIG. 7) to close. This is necessary because the viscosity ofHPLC mobile phases typically are ten times the viscosity of liquidcarbon dioxide so the ball in the HPLC pump check valve falls closedmore slowly. However, it is desirable for the displacement curvature ofthe pump of this invention to have a shorter radius at the end of therefill period to make up for time lost by the larger curvature duringthe depressurization. In the pump of this invention, thedepressurization rate of curvature should be larger than the radius ofcurvature at the end of the refill period, and preferably at least twiceas large. The depressurization displacement from A to C on curve 738should require at least 1.5 times the cam rotation as the samedisplacement on curve 740. Curve 740 corresponds to the displacement ofan ordinary single piston HPLC pump such as an Isco model 2350. For theCO₂ pump during refill, during displacement C to E the averagedisplacement slope is at least 20% greater than that of such an HPLCpump.

As an example, for a pump with 80 microliters of dead volume and 120microliters displacement with a 15 mm (millimeter) stroke, Table 1provides the preferred cam follower and plunger displacement rates orslopes with respect to cam rotation for plunger positions correspondingto the top dead center position through the position at whichdepressurization ceases and inspiration of new liquid starts.

The preferred displacement slope shown in Table 1 is obtained from curve738 (FIG. 9) as follows: (1) row 1--7500 divided by 7500 equals 1; (2)row 2--7500 divided by 4460 equals 1.68; (3) row 3--7500 divided by 2400equals 3.12; (4) row 4--7500 divided by 1350 equals 5.56; and (5) row5--7500 divided by 870 equals 8.62.

In Table 1, carbon dioxide is at 15° C. The relationship betweenpressure and volume was determined from tables in K. S. Pitzer et al.,J. Am. Chem. Soc., 77 3433 (1955). The relative delivery rate(displacement slope) just before position A is "S". Positions justbefaore and just after A are referred to as A - and A +. Between thesetwo locations, the cam surface is greatly rounded and the slope is zeroat A. The calculation is based on isothermal expansion and does not seemto produce a large error.

                  TABLE 1                                                         ______________________________________                                                                         Preferred                                                            Pressure Displacement                                                         in pump  slope (curve                                 Cam follower            chamber  738 from A +                                 displacement   Volume   PSIG     to C on FIG. 9)                              from position  in pump  from     During fluid                                 A + to         chamber  Pitzer,  delivery                                     position C     ul       et al.   slope = S.                                   ______________________________________                                        Position  0%       80       7500   -S                                         A +      25%       85.1     4460   -1.68S                                     Position B                                                                             50%       90.2     2400   -3.12S                                              75%       95.4     1350   -5.56S                                     Position C                                                                             100%      100.5     870   -8.62S                                     ______________________________________                                    

In FIG. 10, there is shown an air-cooled inlet fluid heat exchanger 762similar to the heat exchanger 763 (FIG. 7) for the pumphead and thecooling assembly 306. The heat exchanger 762 includes a spiral coil 742,an aluminum disk 744 and aluminum disk 746 and a thermoelectric coolingelement 754. The thermoelectric cooling element 754 pre-cools fluidentering the spiral coil 742 through tubing 770 connected to the coil742 before the fluid reaches the inlet valve fitting 310 of pumping unit12 (FIG. 7) through tubing 772 that connects the inlet valve fitting 310(FIG. 7) to the coil 742.

The spiral coil 742 has 0.06 inch outside diameter by 0.04 inch insidediameter and is formed of stainless steel tubing sandwiched betweenaluminum disks 744 and 746. A bore of 0.04 inch is unusually large forthis size tubing. The spiral coil 742 is in close thermal contact withdisks 744 and 746 because of thermally conducting compound packed in theinterstitial spaces such as indicated at 748. A screw 750 compressesaluminum disks 744 and 746 together, but a heat conducting aluminumspacer 752 prevents serious flattening of spirally wound tubing 742.

The aluminum disk 744 is in good thermal contact with one side ofthermoelectric cooling element 754 and with disk 746 through spacer 752.The thermoelectric cooler 754 is the same type as thermoelectric cooler386 (FIG. 7). The second side of thermoelectric cooling element 754 isin good thermal contact with finned aluminum extrusion 392. The finnedaluminum extrusion 392 is enclosed by sheet metal shroud 394 whichdefines forced air cooling passages between the fins such as 396. Fourscrews 756A-756D (only 756B and 756D being shown in FIG. 10) compresslow thermal conductivity plastic. clamping members 758A-758D (only 758Band 758D being shown in FIG. 10) against disk 746 by means of clampingforce supplied by screws 756A through 756D and spring washers 760A-760D(only washers 760B and 760D being shown in FIG. 10) under the heads ofthese screws. The screws are threaded into the finned extrusion 392 andtightened sufficiently so that thermal contact on both sides ofthermoelectric cooler 754 is obtained. The screws 756B and 756D, springwashers 760B and 760D, and clamping members 758B and 758D appear in FIG.10. The other two sets are out of the plane of the section and do notappear on this figure.

The assembly formed of disks 744 and 746 and spiral coil of tubing 742sandwiches thermoelectric cooling element 754 against finned aluminumextrusion 392 because disks 744 and 746 have four-point spring loadedclamping. Passing a current through thermoelectric element 754 causesthe side of thermoelectric element 754 that is adjacent to disk 744 todraw heat from disk 744 thereby cooling it and cooling the spiral coilof tubing 742 and cooling the contents of the tubing within this spiralcoil. Heat absorbed from aluminum disk 744 and electrical heat generateddue to electrical resistance of the thermal elements withinthermoelectric cooling unit 754 is rejected to finned aluminum extrusion392. The heat is removed from finned extrusion 392 by air flow throughthe cooling passages, one of which is labeled 396, such air flow beingin the direction into the plane of the paper. Note that liquid coolingis not used in any form.

The cooled length of the spiral wound coil of tubing 742 within heatexchanger 762 is 75 inches. With the tubing's internal diameter of 0.04inch, this results in a heat exchanger volume of 1.5 milliliters. Thevolume of the heat exchanger should not be much less than twice thedisplacement of the pump 12, or largely uncooled liquid will shootrapidly through the heat exchanger without adequate cooling during theinlet stroke of the pump. This makes the heat exchanger ineffective.

Increasing the heat exchanger volume to greater than twice the pumpdisplacement further improves the efficiency of the heat exchanger,especially at flow rates greater than two milliliters per minute, due tothe longer fluid contact time in the heat exchanger. In the preferredembodiment, the 1.5 milliliter heat exchanger volume is greater than tentimes the 0.12 milliliter displacement of the pump. The length todiameter ratio of the wetted surface of the heat exchanger as describedin the preferred embodiment is 1875 to 1. This provides a large contactarea-to-volume ratio which efficiently cools the liquid, e.g. carbondioxide, being pumped. For acceptable efficiency, the length to diameterratio should be at least 50 to 1. Non-circular cross section heatexchangers should have a surface to volume ratio at least equal to thatof a tube with a 50 to 1 length to diameter ratio.

In FIG. 11, there is shown a pumping system 1100 with pumphead block 300(rest of pump not shown in FIG. 11) and the in-line heat exchanger 762mounted to cooling assembly 306. A shrouded (box type) propeller fan 764pulls outside air into the air passages 396 (FIGS. 7 and 10) of finnedaluminum extrusion 392 as shown at 766. The fan 764 may be a Nidec#A30108 which produces an air flow of about 95 cfm at a static pressureof 0.05 inch of water. The air exits the passages 396 and is exhaustedby the fan shown by the arrows 768. This, in cooperation with anelectric current passing through thermoelectric cooling elements 386(FIG. 7) and 754 (FIG. 10), cools the in-line heat exchanger 762 and thepumphead block 300.

In operation, liquid near its supercritical point enters the heatexchanger 762 through tubing 770, is cooled in its inward spiral passagethrough spiral coil 742 (FIG. 10) and exits the heat exchanger throughtubing 772. Tubing 772 is connected to the tubing fitting located withinthreaded recess 320 (FIG. 7) of inlet check valve assembly 310 (FIG. 7).

To prevent liquid from warming up in its passage from heat exchanger 762to pumphead block 300, tubing 772 is fitted with tubular thermalinsulation 774 and the efficiency of cooling of heat exchanger 762 isimproved by its insulated covering 776. Moreover, the efficiency ofcooling of pumphead block 300 is improved by the cylindrical wrap offlexible insulation 778.

Thermoelectric coolers 386 and 754 are connected electrically in seriesand powered from a d.c. power source (not shown) at 2.5 amperes andabout 11.5 volts each for Melcor CP1.0-127-05L. thermoelectric elementsor 3.8 amperes at 7.7 volts each for Melcor type CP1.4-127-045Lthermoelectric elements. The Melcor CP1.0-127-05L thermoelectricelements pump about 14 watts of heat and the Melcor type CP1.4-127-045Lthermoelectric elements pump about 16 watts of heat under theseconditions. Both thermoelectric elements require the same amount ofelectric power to do this, which is 29 watts.

In FIG. 12, there is shown a simplified elevational view of a pumpingmodule 780 having the motor 726, a transmission 792, the cam 338, thecam follower 342, the pumphead block 300 and the cooling assembly 306.The motor 726 is connected to the cam 338 through the transmission 792to drive the cam 338 and cam follower 342 to operate the pump asdescribed in FIG. 7. Threaded stainless steel studs 715 and 717 (FIG.12) hold pumphead block 300 to mounting sleeve 378 with plastic supportblock 376 sandwiched between the pumping block and the mounting sleeve378. The mounting sleeve 378 carries tapped holes for the studs and fitstightly within molded plastic pump body 782.

As described earlier, tubular slide 348 reciprocates within the bore ofmounting sleeve 378. Its reciprocating motion is driven by rotating cam338 which is in contact with roller bearing cam follower 342 which issupported by trunnion 344 (FIG. 7) located within the two yokes 346(FIG. 7) which are an integral part of tubular slide 348. The cam 338 issupported by shaft 382 which in turn are supported by ball bearings 784and 786.

Advantageously, the profile of the cam corresponding to the fluiddelivery portion of its rotation is a linear spiral. The bearing 786 ismounted on removable plate 788 which is fastened to the plastic pumpbody 782. A hub 790 on shaft 382 carries optical flag 722 whichcooperates with sensor 724 mounted on plate 788 which in turn isfastened to pump body 782.

As shown in FIG. 12, the flag location at 722 corresponds with theposition of the cam as shown. When the cam rotates about 90 degrees, itis in the position which causes outward excursion of rod 304 sufficientfor the rod to fill about half the length of sleeve 364 (FIG. 7). Thisposition of the flag is shown by the phantom lines at 800. At thisposition, the flag 722 blocks the sensor 724, which produces an outputsignal indicating the aforementioned rod position. At about maximumoutward excursion of the rod 304, the flag unblocks the sensor 724,providing an indication of essentially the end of fluid delivery fromthe pump chamber 336 (FIG. 7).

The transmission 792 includes a twelve-to-one reduction gear box thatcouples cam shaft 382 to the left shaft extension (not shown) of shaft794 of drive motor 726. The drive motor 726 runs faster than shaft 382.The gear box is partially filled with oil to improve life of itsinternal moving parts. This oil is retained by a tight-fitting gear boxcover.

The visible end of the shaft 794 carries hub 796 which supportstachometer disc or encoder 798. Disc 798 is also shown in FIG. 15. Nearits periphery, tachometer disc 798 (FIG. 12) carries a number of holes804 (200 holes are convenient) which cooperate with optical sensor 1454Ato produce a pulse repetition rate proportional to angular velocity ofthe rotor of motor 726 and its tachometer disc 798. Optical sensor1454A, which produces this repetitive pulse, is mounted on bracket 805which in turn is fastened to motor 726. The motor 726 may be a Pittmantype 14205B749 24 volt d.c. motor.

With the above arrangement, a higher flow rate at any pressure includingthe maximum pressure of 7500 psi is provided than in a dual pumpingsystem with the same individual kinds of components: insulatedpumpheads, insulated heat exchanger, thermoelectric cooling elements,heat rejection means and cooling fans but with two pumping unitssimultaneously running in parallel. The head of one such pumping unit isthermoelectrically cooled but its inlet line is not cooled. The secondsuch pumping unit is not cooled, but its inlet fluid is cooled by theheat exchanger. The two pump flows are added together and measured. Thedual pumping system requires two of the relatively expensive pumpingunits rather than one, but has inferior performance. Thus, betterresults are obtained with fewer components even though, under a commoncorollary of the second law of thermodynamics sometimes referred to as"law of diminishing returns", the whole is, at most, equal to the sum ofits parts; and usually is equal to less than the sum of its parts forthermal systems. The whole being less than the sum of its parts isparticularly true when cascading thermal processes, such as the twostages of thermoelectric cooling. This is a surprising result. Moreover,the above described arrangement provides more predictable results andlacks erratic characteristics found in an arrangement having separatecooling arrangements.

In FIG. 13, there is shown a simplified schematic view of the pumpingsystem and a measuring system connected together for measuring flowrates and/or pressure and having for this purpose a pumphead block 300,an inlet valve 310, and an outlet valve 308, pressure transducer 948 formeasuring the pulsating pressure associated with the pumping system 12and a flowmeter 957 for measuring flow rates. There are at least twoways of measuring this pulsating pressure and at least two ways ofmeasuring the flow rates.

To measure the fluctuating pressure within the pumping chamber 336 (FIG.7) during the stroke cycle of the plunger rod 304 (FIG. 7), the frontface of the pumphead has a counterbore 936 which leaves a relativelythin layer of metal 940 between the bottom of the counterbore 936 andthe end of pump chamber 934. The thickness of the diaphragm thus formedat the bottom of the counterbore 936 must be sufficient to withstand themaximum pressure within the pumphead 300 at the fatigue endurance limitof the pumphead material.

A diaphragm pressure transducer strain gauge element 938 is cemented tothe central portion of the thin layer of metal 940 at the end of thecounterbore 936. The electrical leads 942 from gauge 938 are extended toa conventional differential amplifier (not shown in FIG. 13) whichproduces an output signal on (not shown) proportional to pressure withinthe pumphead.

Alternatively, commercially available flow-through pressure transducer948 is connected to the outlet line 952 of pumphead 300 with the valve965 closed and the valve 969 open to avoid flow to the flowmeter 957.The pressure fluctuations here are less and do not completely correspondto the fluctuations within the pumphead because of the action of outletcheck valve assembly 308 (FIG. 7). Conductors 950 from the pressuretransducer 948 are connected to a conventional differential amplifierwhose output is proportional to the fluid pressure in pump outlet line952. Line 959 conducts fluid to the utilizing apparatus such as asupercritical fluid extractor (not shown).

The pressure sensed by diaphragm strain gauge element 938 drops to thepressure in inlet line 930 during the refill stroke of the pump. Thepressure sensed by pressure transducer 948 on the pumphead outlet line952 does not generally drop either to zero or to the inlet pressureduring the inlet stroke of the pump. This is because, although outletflow from the pump stops during the inlet stroke, the pressure stored bythe compliance of the compressible fluid in the high pressure fluidsystem connected to the outlet line maintains the pressure at a highlevel. However, there is some small to moderate decrease in pressureduring the inlet stroke if fluid is flowing to an outlet, as forexample, to supply a supercritical fluid extractor at moderate or highflow rate. At very low flow rate, if the extractor has a large internalvolume, the decrease in pressure may not be enough to be useful. In sucha case, recourse is made to measurement of flow changes instead ofpressure changes.

To measure changes in flow in one embodiment, outlet line 952 isconnected to outlet fitting 308 of pump 300, the pressure transducer 948is connected to line 952 through line 951, line 953 is also connected toline 952 and leads to capillary restrictor 957. Valve 965 is open and967 is closed. Fluid flows from the pump outlet fitting 308 throughlines 952, 953, through restrictor 957, through line 959 and to asupercritical extractor. During fluid delivery, fluid flows from left toright through capillary restrictor 957. This causes the pressure at line953 to exceed that of the pressure in the supercritical extractor. Thisflow-induced pressure rise sensed by pressure transducer 948 isindicative of delivery of fluid from the pump.

At sufficiently high flow rates, the pressure drop across restrictor orflowmeter 957 may become inconveniently high. The pressure drop may behigh enough to noticeably decrease the flow from the pump, especially athigh extraction pressures. A spring-loaded check valve 961 may beconnected across the restrictor or flowmeter 957. This check valve canbe set to crack open at a convenient pressure such as 50 or 100 poundsper square inch, so that the restrictor 957 does not increase the headpressure seen by the pump 300 by more than this amount at high flowrates.

In another embodiment, a thermal flowmeter is included at 957 to measureflow from the pump 300 to the supercritical extractor and the valve 967is closed. Flow from the outlet to the pump flows through lines 951 and953 to an electrically insulated coupling to a conventional thermal flowsensing tube. The flow sensing tube is coupled by another electricallyinsulated coupling to line 959 to the inlet of the supercriticalextractor.

Preferably, the electrically insulated tube is made of a metal having arelatively high temperature coefficient of electrical resistance. Itsinside diameter should be no more than that necessary to carry themaximum desired flow without increasing the head pressure seen by pump300 to a point where it produces a noticeable degradation in maximumflow rate at maximum operating pressure. This tube should have a lowthermal mass, so its wall thickness should be no more than necessary toreliably sustain maximum operating pressure.

Electrical leads couple a conventional electrical readout device to theends of the electrically insulated tube. The readout device produces anelectrical current which flows through the electrically insulated tube.This current is of sufficient magnitude to appreciably heat the tubewhen there is no flow through the tube. The tube cools down in responseto flow coming from pump 300. Flowing fluid removes heat from the tube,which is warmer than the fluid. This drop in temperature decreases thetube's electrical resistance which is sensed by the electrical readoutdevice. An electrical output from the readout device may be used inplace of the electrical readout from the pressure transducer 948.

If at the maximum desired flow rate the pressure drop across the tube isenough to noticeably degrade the performance of pump 300, spring-loadedcheck valve 961 may be connected in parallel with it. With thisarrangement, the pressure seen by pump 300 never exceeds the pressure atthe inlet of the supercritical extractor plus the cracking pressure ofthe spring-loaded check valve 961. If rapid response is required tosense the start of a flow having a very low flow rate, it may bedesirable to use a readout device that maintains the sensing tube at aconstant temperature, and in which measurement is made of the voltage,current or power required to keep the tube at such constant temperature.This measurement indicates flow. Controllers for keeping a flowing fluidfilled tube at constant temperature are described in U.S. patentapplication Ser. No. 08/027,257, now U.S. Pat. No. 5,268,103 APPARATUSAND METHOD FOR SUPERCRITICAL EXTRACTION, Daniel Gene Jameson, et al.

A further refinement is to divide the sensing tubing into two sectionswith the upstream section not being heated and the downstream sectionbeing heated. The temperature of both sections is measured by acontroller and the downstream section is heated to a temperature that isa constant amount warmer than the upstream section. This providesgreater reliability over a wider range of flow rates, ambienttemperatures and fluid supply temperatures.

In FIG. 14, there is shown a schematic circuit diagram of a firstmeasuring circuit 991 for accurately determining the flow of a pump thatpumps a very compressible liquid by measurement of pumping conditions.For this purpose, the measuring circuit 991 includes, as its principalcomponents, a double differentiator or differentiating amplifier 992,AND gate 1053, optical approximate-dead-center sensor 998, invertedpulse former 1156, AND gate 1158, invertor 1164, AND gate 1168 and atachometer sensor 1454A.

To determine the rate of flow from the end-of-stroke information and thestart-of-fluid-delivery information according to a first method andusing circuit 14, a pressure signal from pump chamber pressuretransducer element 938 is applied to the double differentiator 992 onconductor 990, and in response, the double differentiator 992 transmitsa pulse on conductor 996 to one input on AND gate 1053. The pump 300(FIGS. 12 and 13) is equipped with optical approximate-top-dead-centersensor 998 (FIG. 14). This sensor has its light emitting diode currentset by resistor 1150 and load resistor 1152 senses the current.

This potential drop across load resistor 1152 representing current flowproduces a voltage on conductor 1154 which is at a logic high levelexcept during the time that flag 722 (FIG. 12) breaks its light path.The following re-establishment of this light path produces a logic-highlevel which is applied to inverted pulse former 1156.

The pulse former 1156 produces a logic-low level pulse of 5 microsecondduration which corresponds to the onset of the approximate top deadcenter condition. The low voltage on conductor 1061 appears at an inputof AND gate 1158. AND gates 1053 and 1158 are connected R-S flipflop byleads 1054 and 1055.

When the double differentiator 992 applies a negative pulse to inputlead. 996 of this R-S flip flop, the conductor 1162 latches to logiclow. This low is conducted to the input of invertor 1164 whose output1166 goes positive. This enables AND gate 1168 so that it accepts thepulse train on conductor 1160.

This pulse train on conductor 1160 is derived from tachometer sensor1454A which monitors the motor speed via tachometer disc 798 (FIGS. 12and 17). A resistor 1172 sets the current through the light emittingdiode of optical sensor 1454A and current through the phototransistor ofsensor 1454A flows through resistor 1174 which produces the train ofvoltage pulses corresponding to the passage holes 804 (FIG. 12) oftachometer disc 798 passing through the light path of optical sensor1454A. As AND gate 1168 is enabled when output 1166 is high, the gate'soutput lead 1176 produces gated tachometer pulses representing flowvolume during fluid delivery from pumphead 300.

At the end of the delivery stroke, approximate top dead center sensor998 senses the passing of optical flag 722. (FIG. 12) on cam shaft 382(FIG. 12), producing logical high level on lead 1156 and a logic lowpulse on lead 1060. This resets R-S flipflop composed of NAND gates 1053and 1158, putting logic high level on lead 1162 and invertor 1164, andtherefore a low level on 1166, shutting off AND gate 1168 and stoppingthe pulse train on 1176.

The number of pulses in the train of pulses corresponding to each strokeof piston 304 and appearing at the output 1176 of NAND gate 1168 isproportional to high pressure fluid delivery from the pump during thatstroke. Other pulses are available from this logic circuit. The pulsetrain at lead 1066 corresponds to the continuous tachometer signalrepresenting the entire operating dynamic speed range of the pump motor726 (FIG. 12). The output on lead 1204 from invertor 1062 goes to alogical high during the time that the optical flag 722 (FIG. 12) stopsinterrupting the optical sensor (corresponding to sensor 724 on FIG.12). This logic high level starts at the time the cam 338 reaches topdead center. NAND gate 1072 produces an output on lead 1074 that is thecompliment of the output on the lead 1176. The lead on 1074 is the pulsetrain representative of that part of the drive motor rotationcorresponding to no flow from the pumphead.

For example, it is desirable to know the flow rate when pumping atconstant pressure, which is often the case with supercritical fluidextraction systems. The typical pressure within pumping chamber 336(FIG. 7) of pumphead 300 during a complete stroke cycle, starting withthe plunger rod 304 having been moved all the way to the left (minimumdisplaced volume) is 6000 psi.

The pump cycle then includes the rod 304 relatively rapidly movingtoward the right to refill the pumping chamber, and then moving backagain more slowly to the left to repressurize the pumping chamber and todeliver fluid from the outlet of the pump. A typical, though by no meanslimiting, operating pressure is 6000 pounds per square inch. Pressurewithin the chamber 336 starts at 6000 pounds per square inch during thefinal stages of a previous delivery stroke, at which time the piston 304reverses and the pressure drops toward the inlet pressure which istypically 800 psi, the vapor pressure of carbon dioxide at roomtemperature.

The pressure in the chamber 336 is at 870 psi in the preferredembodiment when the pump chamber fills through check valve 310 (FIG. 7)connected to the inlet line leading to the source of suitable liquidsuch as liquified carbon dioxide. The rod 304 reaches its maximumrightward excursion, refilling stops, and the rod starts to return tothe left, compressing liquid carbon dioxide ahead of it. The pressureduring this time rises from its lowest level.

When the pressure within the pumping chamber 336 reaches the pressure ofthe outlet line and whatever system is connected to it, the check valve308 opens. The pressure within the pump chamber 336 when outlet checkvalve 308 is open, during fluid delivery, is a few percent lower thanthe 6000 pounds per square inch at the end of the previous stroke. Thisis because the fluid using system has drained some of the fluid from thehigh pressure line and its associated fluid holding components therebydropping the pressure.

During the delivery stroke, the pressure gradually rises until at theend of the delivery stroke, the pressure is back to the original 6000pounds per square inch. At this time, the plunger rod 304 has completedthe leftmost portion of its stroke and starts to retract. This causesthe pressure to drop, repeating the cycle described. The pressure duringthe fluid delivery period varies only slightly during the stroke. Theaverage pressure can be considered a close approximation to constantpressure. If the velocity of the piston rod 304 is integrated over thedelivery time, the result is the volume delivered per completestroke-cycle of the piston 304.

If the portion of cam 338 (FIG. 7) corresponding to the delivery strokeof (leftward stroke) of the rod 304 is a linear spiral then theintegration for determination of flow per pump stroke can beaccomplished by integrating the pump drive motor speed over the deliverytime. The terminal part of this interval is easily found as itcorresponds to the top dead center position of cam 338 or it can betaken as the time that the pressure in the pump chamber 336 stopsrising. The former may be determined by the output of sensor 1454A (FIG.12) which produces a signal from optical flag 722 (FIG. 12)corresponding to near top dead center location of the plunger rod 304.Measurement of the motor speed for the integral is easily accomplishedby counting the pulses in the pulse train produced by optical sensor1454A (FIG. 12) in cooperation with tachometer disc 798 mounted on theshaft 794 of motor 726 which drives cam 338 through gear box 792.

The significant problem is to determine the time at which fluid deliverybegins on each cycle of plunger rod 304. This is convenientlyaccomplished by single or double differentiating the pumphead pressuresignal versus time. A first differential corresponds to the initialincreasing downward slope of pressure during a refill. The signal levelsoff after falling because of the saturation limit in the electronics ofthe differentiator.

The signal gradually increases as the pressure increases during the timethat fresh liquid carbon dioxide flows through the inlet check valveinto the pump chamber 336 and then generally linearly increases as theleftward motion of piston 304 builds pressure up within the pumpingchamber 336. The signal then decreases in rise as pressure decreases isrise within the pumping chamber when the outlet check valve 308 opens atthe time the pressure in the pumping chamber slightly exceeds thepressure in the outlet line. The signal increases slowly correspondingto the few percent increase in pressure during delivery until a drop atthe beginning of the next pump cycle.

The first differential or first derivative of the pressure in the pumpchamber can be used to detect the end of a pump delivery stroke as thesignal goes from a small positive value to a larger negative value. Thisinformation may be used interchangeably with the signal from theend-of-stroke sensor 724 (FIG. 12). It can also be used to detect thebeginning of fluid delivery on the next stroke as the differentialsignal goes from a larger positive level to a lower positive level.

The second differential or the second derivative provides a negativepulse that corresponds to the downward slope of the first derivative anda positive pulse that corresponds to the upward slope of the firstderivative. The first derivative corresponds closely with informationderived from the optical sensor flag 722 (FIG. 12). The secondderivative negative pulse occurs just at the time of initiation ofdelivery and therefore can be used to start the integration processwhich determines delivery per pump stroke.

When making a flow rate determination by a second method, the outputpressure or flow of the pump by pressure transducer 948 or thermalflowmeter 957 is monitored (FIG. 13) instead of measuring the headpressure of the pump with diaphragm transducer strain gauge means 938(FIG. 13). Assuming that the pressure transducer 948 is used to effectthis method, that the pressure at the output of the pump at the start ofa stroke is 6000 psi and that the piston is at the end of its previousstroke, then the pump passes top dead center, it first depressurizes theremaining liquid trapped within the pumphead, then inspirates additionalliquid from the supply reservoir, and finally, the rod 304 (FIG. 7)repressurizes the inspired liquid to the delivery pressure. During thistime, the pressure at the outlet of the pump as sensed by transducer 948(FIG. 13) is dropping because of demand from the connected system suchas a supercritical fluid extractor.

Typically, the pressure drops a few percent during this time. If theinitial pressure is 6000 psi, the pressure may drop to say, 5850 psi. Atthis point, the content of pump chamber 336 (FIG. 7) is repressurized tothe point where it slightly exceeds the head pressure and outlet checkvalve 308 (FIG. 7) opens admitting pressurized fluid to the outlet line.The pressure gradually rises from its starting level to its final levelof 6000 psi. The integration points can be determined with a singledifferential (single time derivative) instead of a double derivative andprocessed and used as described above.

The pressure signal on the conductors 950 (FIG. 13) from pressuretransducer 948 is amplified by a differential amplifier (not shown) andconveyed to a single inverting differentiator. A suitable doubledifferentiator for 992 (FIG. 14) is described in U.S. Pat. No.4,882,063. A suitable single inverting differentiator is derived fromhalf of the double differentiator shown in U.S. Pat. No. 4,882,063. Thelogic circuitry is the same as in FIG. 14 when a single invertingdifferentiator is used and produces signals including the gatedtachometer pulses on lead 1176 representing flow volume during the timethat there is fluid delivery and pulses during the time that there is nofluid delivery. Gated output pulses representing flow are available onlead 1176.

To use flow sensor information instead of pressure information, todetect the start of fluid delivery for each stroke, a signalrepresenting flow information based on information from pressuretransducer 948 in conjunction with a capillary restrictor (FIG. 13) orfrom information relating to the resistance of the sensing tube inthermal flowmeter 957 (FIG. 13) or the power supplied to the sensingtube by electrical sensing unit in flowmeter 957 is high during times offlow from forcing fluid through the capillary restrictor or the powersignal is at a higher power level for the heating tube in flowmeter 957to keep it a constant temperature as the flow carries heat away. Sincethis signal is not zero-based, it either needs to be adjusted withrespect to a zero level by conventional fixed or tracing means ordifferentiated by a conventional differentiator.

The latter will be used for the purpose of this explanation. The firstdifferential of this signal is a short spike that appears at the outputof differentiator 992 on line 996 (FIG. 14). This signal is applied tothe input of RS flip-flop element 1053 and operated upon gatedtachometer pulses on indicating pump displacement during periods ofdelivered flow and gated tachometer pulses on lead 1074 when there is nodelivered flow.

In an alternative to the embodiments already described in regard toFIGS. 13 and 14, flow can be determined by integrating cam or drivemotor rotation over the depressurization, inlet and repressurizationtime 396, and subtracting this from the known constant integralcorresponding to a full cam rotation. It is also often desirable to pumpat constant flow rate, which is difficult to do with any accuracy if thefluid is highly compressible.

In FIG. 15, there is shown a constant flow controller 1200 forcontrolling the pump motor speed for constant flow regardless of fluidcompression, using the gated pulses relating to flow from thearrangements of FIGS. 13 or 14. These tachometer pulses cannot be usedas feedback to directly control a servo-operated pump motor. This isbecause the discontinuous nature of the pulses would cause the pumpmotor rotor to jump and buck while it is running over the pumping cycle.

As shown in FIG. 15, the gated tachometer pulse train can be used tocontrol the setpoint voltage for a motor velocity control servo for thepump. It controls the motor speed to a constant value which is updatedafter each pump stroke. The same sort of scheme can be used to controlan updated motor rotor angle location for a position control servo. Thebasic idea is to divide the setpoint voltage (or digital setpointsignal) by an amount equal or proportional to that part of therevolution time of the cam 338, which occurs during actual delivery offluid. The latter is proportional to the number of gated flow pulses perstroke. Equations 1-8 together are a mathematical explanation of whythis division is made.

In the operation of the embodiment of FIG. 15, at the end of a precedingdelivery stroke, the voltage on lead 1063 goes high for 5 microseconds.This is applied to OR gate 1102 which ensures that no pulses whicherroneously may be on lead 1075 are transmitted through lead 1103 to theclock input of 12-bit binary counter 1104. After a 1.6 microsecond delayprovided by resistor 1106, capacitor 1107 and Schmidt inverter 1108,lead 1112 goes negative. OR gate 1113 in cooperation with resistor 1109,capacitor 1110 and inverter 1111 produce a 600 nanosecond low logiclevel pulse on lead 1116 which is connected to the "write" inputs ofdigital-to-analog converter 1118.

A flow rate setpoint voltage "V_(S) " is applied to the feedbackresistor port (lead 1125) of converter 1118. The counter 1104 is a type4040B and the digital analog converter is a type DAC1210. The logic lowpulse on lead 1116 causes digital-to-analog converter 1118 to read andstore the 12-bit pulse count signal on 12-bit line 1117. The output ofOR gate 1113 on lead 1114 is also conducted to OR gate 1136 which incooperation with resistor 1132, diode 1133, capacitor 1134 and inverter1135 produces a 600 nanosecond positive pulse on lead 1105. This resetscounter 1104 to zero.

The start of the next train of gated flow pulses from AND gate 1168 inFIG. 14 occurs after all of the logic voltage levels are back to theirnormal low level. Flow pulses are conducted on lead 1075, through ORgate 1102 and into the clock input of counter 1104. The counter countsthese flow pulses and completes an output on 12-bit binary coded lead1117 at the end of fluid delivery when the flow pulses stop. This outputis then entered into the digital to analog converter 1118 when lead 1116goes low as described above. This process repeats for every stroke ofthe pump, providing an updated motor speed setpoint at the end of everystroke as will be described below.

Operational amplifier 1126 may be a type 308A. The output lead 1127 ofamplifier 1126 is connected by lead 1123 to the reference port ofconverter 1118. Digital to analog converter 1118 and operationalamplifier 1126 are connected so that the analog input voltage V_(S) isdivided by the 12-bit binary number on lead 1117. This is in accordancewith FIG. 14 and its accompanying explanatory information found on page4-70 of National Semiconductors Linear Databook 2, Rev. 1, 1988 Edition.##EQU1##

The output voltage on lead 1123-1127-1128 is proportional to V_(S)divided by a number proportional to the number of gated flow pulses perstroke. This is in accordance with Eq. 8, and is the control voltagewhich sets the speed of the pump motor. The voltage is updated afterevery delivery stroke. It is applied on lead 1128 to the conventionalvelocity servo composed of servo amplifier 1129, pump drive motor 726,shaft 1150, pump 780, shaft 794, tachometer 798, sensor 1454A, andfrequency-to-voltage converter 1130 which closes the servo loop.

The pump speed is kept proportional to the control voltage by servoaction. This keeps motor speed and pump speed at a rate which produces aflow rate directly and constantly proportional to flow rate setpointvoltage V_(S).

Instead of the constant flow rate operation described above, the pumpmay be run in constant pressure operation. Constant pressure circuitryis known in the art. Examples include U.S. Pat. Nos. 3,985,467 and4,775,481. It is desirable to have a supercritical fluid supply systemcapable of metering or proportioning in other fluids to modify theproperties of the supercritical fluids. An example of doing this withconstant flow operation is U.S. Pat. No. 3,398,689. An example of doingthis with constant pressure operation is found in U.S. patentapplication Ser. No. 07/843,624 by D. G. Jameson and R. W. Allington,filed Feb. 27, 1992, now U.S. Pat. No. 5,360,320, the disclosure ofwhich is incorporated herein by reference.

For constant pressure operation, it is useful to know the actual flowrate. In FIG. 16, there is shown a flow rate indicator/controller 1400which accomplishes this utilizing the gated flow pulses on lead 1075 andcam revolution pulses on lead 1063. It will be appreciated that theactual flow rate is equal to flow quantity per unit time andproportional to the number of gated flow pulses during a cam revolution,per revolution time of the cam 338.

Gated pulses representing actual flow quantity are delivered on lead1075 (FIG. 15 and 16) to counter 1407 during one stroke of the pump. Atthe end of fluid delivery for that stroke, the output of the counter onlead 1408 represents the fluid delivered. This output is led to thenumerator input of divider 1403. Five microsecond pulses representingthe completion of each revolution of the cam 338 are lead on lead 1063to the input of integrator 1401.

The output on lead 1402 of integrator 1401 represents the time for cam338 (FIG. 7) to make one revolution. During the five microsecond pulseon lead 1063, the integrator 1401 and the counter 1407 freeze or holdtheir outputs constant. The integrator 1401 and counter 1407 reset justafter each pulse on lead 1402. The output on lead 1402 is connected tothe denominator input of divider 1403, so the output of the divider onlead 1408 corresponds to the flow rate during the five microsecond pulseon lead 1063. During this time, sample and hold 1406 stores the flowrate signal on lead 1408 because it is activated by the five microsecondpulse on lead 1404.

A flow rate signal relating to the immediately preceding pump stroke ispresent at the sample and hold output lead 1407. The flow rate signal onlead 1407 is led to display 1410 which displays actual flow rateregardless of whether the pump is operating in a constant flow mode or aconstant pressure mode. This signal may also be used for controlpurposes, as in the control of a fluid modifier pump which metersmodifier fluid into a supercritical fluid in selected proportion to theactual supercritical fluid flow rate regardless of whether the pump isoperating in a constant flow mode or a constant pressure mode. Asupercritical fluid flow rate signal for such proportional control isavailable on lead 1411.

In FIG. 17, there is shown the use of the gated flow pulse generator1100 (also see FIG. 15) and the flow rate indicator/controller 1400(also see FIG. 16) in a constant-pressure supercritical fluid extractionsystem for the purpose of controlling a fluid modifier pump so that itmeters modifier fluid into the inlet of the supercritical fluid pumpingsystem 1570 (FIG. 17) in selected proportion to the rate at whichsupercritical fluid enters the inlet of supercritical fluid extractor1580.

A tank 1501 supplies liquid carbon dioxide 1501A through valve 1502 andinlet line 1503 to the inlet line, check valve 1504. The outlet of checkvalve 1504 is connected to line 1505 through a first arm of tee 1506,out a second arm of tee 1506 to a Bourdon tube or other pressurepulsation damping and fluid storage device 1512. The outlet of Bourdontube 1512 is led through line 770 to pre-cooling heat exchanger 762(FIG. 11). The outlet of this heat exchanger is led through line 772(FIG. 11) to the inlet of reciprocating pump 780 (FIG. 12). The pumpheadblock of pump 780 and the pre-cooling heat exchanger 762 (FIG. 11) arecooled by thermoelectric elements (not shown) which are thermallyconnected to heat rejection means 306 which is directly air-cooled byfan 764 (FIG. 11). The items 762, 780, and 306, and the thermoelectriccooling elements are as described hereinabove.

The outlet of pump 780 is connected by line 952 (FIG. 13) to the inletof flow-through pressure transducer 948 (FIG. 13). The outlet ofpressure transducer 948 is connected by line 944 (FIG. 13) to the fluidinlet of supercritical fluid extractor 1580 which may be one of thetypes of supercritical fluid extractors described in the parentapplication. An electrical signal from pressure transducer 948 (FIG. 13)indicating fluid pressure in line 944 (FIG. 13) is carried by lead 906(FIG. 13) and 906C to constant pressure pump control 1590. The control1590 may be of one of the types of known constant pressure pump controlsreferenced earlier in this disclosure.

The control output of constant pressure control 1590 is conducted onlead 1597 and power drive motor 726 (FIG. 12) of pump 780. The drivemotor 726 is equipped with tachometer means (not shown) which suppliesan electrical signal indicative of its rotational speed on line 1066 togated flow pulse generator 1100 and on line 1066C to constant pressurepump control 1590. The pump control 1590 may use motor rotational speedand position information and pump outlet pressure information to controlpump speed to obtain constant pressure in accordance with knowntechniques referenced earlier. A cam position transducer (722-724 onFIG. 12, not shown on FIG. 16) which is part of pump 780, produces anelectrical signal on lead 1058B indicative of pump cam and plungerposition and supplies this signal to a second input of gated flow pulsegenerator 1100. A signal indicative of fluid pressure in line 944 issupplied to a third input on gated flow pulse generator 1100 on line906E.

As described previously in this disclosure, generator 1100 produces anelectrical output on lead 1063 which is a 5 microsecond pulse indicativeof cam position near the top dead center minimum chamber volume of eachstroke of the pump 780. The second output on lead 1075 from generator1100 is gated pulses which correspond to the rotation of the motor 726and therefore rotation of the cam (not shown) in the pump 780 duringactual flow delivery on fluid lead 952 (FIG. 13) at the outlet of thepump. Leads 1063 and 1075 are connected to the two inputs of flow rateindicator/controller 1400. As described previously in this disclosure,control 1400 produces a voltage on lead 1411 which is proportional tothe actual flow rate of fluid through line 952 (FIG. 13).

Lead 1411 is connected to the input of % modifier adjustor/programmer1550. Adjustor/programmer 1550 may be a conventional potentiometer toscale the voltage on lead 1411 to provide a control signal on lead 1411which is connected to the analog control input of liquid pump 1509.Alternatively, adjustor/programmer 1550 may have program means such asone of the two program channels disclosed in U.S. Pat. No. 3,398,689 toallow programming of the percentage of fluid pumped by pump 1509 withrespect to the total amount of fluid flowing through line 952 (FIG. 13).Liquid pump 1509 may be an Isco Model 2350 HPLC pump which accepts a 0to 10 volt d.c. signal on lead 1528 to control the flow rate produced byits pumphead 1510.

The check valve 1504 prevents back flow of modifier liquid from pumphead1510 into supply tank 1501. This back flow could otherwise happenbecause most of the time the pump 780 is discharging liquid and ratherlittle of the time it is inspiring liquid. During the discharge time,excess liquid from pumphead 1510 is stored by expansion of bourdon tube1512.

The inlet of pumphead 1510 is connected by lead 1508 to solvent selectorand mixer 1540. Solvent mixer and selector 1540 may be an Isco Model2360 composition gradient programmer and former normally intended forHPLC use. At low flow rates in fluid line 952 (FIG. 13) and at lowpercentages of modifier composition, the flow rate in line 1508 will beslow enough so that it would be impractical to use selector-mixer 1540to program a varying modifier composition. The volume of the mixingchamber in an Isco Model 2360 gradient programmer is on the order of 1milliliter and if the flow rate in lead 952 were 1 milliliter per minuteand the desired modifier concentration were 5%, the fluid demand onfluid line 1508 would be only 50 microliters per minute. However,programmable selector-mixer 1540 is very useful for scouting differentmixed modifier compositions during development of supercriticalextraction methods prior to routine use.

The mixer and selector 1540 has three fluid inlet lines 1541, 1544 and1547 which dip into three different modifier liquids 1543, 1546 and 1549contained in flasks 1542, 1545 and 1548. With this arrangement, themixer and selector 1540 blends any combinations of these liquids andsupplies them as an ongoing flow to the inlet of pumphead 1510.

The outlet 1571 of pumphead 1510 is lead to selector valve 1570 which inthe position shown conducts fluid from pumphead 1510 through line 1511to a third arm of tee 1506 where the modifier fluid is mixed with theliquid carbon dioxide, or other liquid which is to be converted byheating, to a supercritical fluid in extractor 1580. When changingsolvent compositions with mixer-selector 1540, the valve 1570 is resetso that the lead 1571 connects to lead 1572 which vents the outlet ofpumphead 1510 to waste. Pump 1509 is then run at a relatively high rateof speed purging its interior fluid wetted volume and the interior fluidwetted volume of mixer-selector 1540 and refilling them with the newlyselected composition of fluid.

By this it can be seen how knowledge of the actual flow rate of liquidentering the extractor 1580 can be used to accurately and repeatablycontrol a desired modifier concentration in the supercritical fluid.

The functions provided by the constant flow controller 1200 (FIG. 15),the gated flow pulse generator e.g., 1100 (FIG. 15) and the flow rateindicator/controller 1400 (FIG. 16) can be realized by discreteelectronic circuitry or by the computer controller referenced in theparent application.

In FIG. 18, there is shown a cross-sectional view of a valve 54A usablein the embodiments of this invention, having a valve body 1001, femalefittings 1002 and 1003, a ball valve assembly 702 and a valve stemassembly 700. The female fitting 1003 is adapted to communicate with thepump 12 (FIG. 1) to receive supercritical fluid therefrom and thefitting 1002 is adapted to communicate with the pressure vessel andfluid assembly 18. The fitting 1003 and 1002, each communicating witheach other through the ball valve assembly 702.

The valve stem assembly 700 is positioned to hold the ball valveassembly 702 closed in one position, thus blocking flow between thefitting 1003 and the fitting 1002 and in another position to release thevalve ball assembly 702 so the fluid may flow from the pumping system 12(FIG. 1) through the valve 54A and into the pressure-vessel andfluid-extraction assembly 18 (FIG. 1).

The ball valve assembly 702 includes passageways 1006, 1007, 1008, 1009and 1010, a valve seat 1013, a valve element 1014 and a cavity 1015. Thevalve seat 1013 is initially machined as a female cone. The valveelement 1014 is spherical and lies conformingly in the seat 1013 when itis forced into the seat as the valve is tightly closed, thereby forminga seal. When the valve is opened, the valve element 1014 may be liftedfrom the seat to permit communication between the fitting 1002 and 1003.

For this purpose, the valve seat 1013 communicates through thepassageway 1008 at the bottom of the valve as a valve inlet and throughthe successively larger passageways 1007 and 1006 to the inlet femalefitting 1003 to receive fluid underneath the valve seat capable oflifting the valve element 1014. The cavity 1015 is located above thevalve element to communicate with the passageway 1008 when the valveelement 1014 is lifted but to be sealed from it when it is closed at itsbottom-most location. The cavity 1015 communicates through thesuccessively larger passageways 1009 and 1010 with the outlet femalefitting 1002 to permit fluid to flow from the female inlet fitting 1003through the female outlet fitting 1002 when the valve element 1014 ispermitted to rise into the cavity 1015 by the valve stem assembly 700.

The valve element 1014 must be harder on its surface and have a higheryield point than the valve seat 1013 and should be at least three timesas hard as the seat 1013 on its surface. It should have a yield point ofmore than two times that of the seat and at least 40,000 psi since itmust retain complete sphericity even though it rotates when it is liftedfrom the valve seat 1013 and is compressed by the stem into the valveseat 1013 when the valve 54A is closed by the stem assembly 700. Thevalve element 1014 must form a relatively large area of the seat toprovide Hertzian line contact in order to form an adequate seal.

The valve seat 1013 is formed of the same material as the valve body1001 and has a yield strength of at least 20,000 psi and preferably ofabout 85,000 psi. It is made of 316 stainless steel bar stock, hardenedto about 85,000 psi yield strength by cold working to a 20 percentreduction in area. With this method of forming, the valve itself and thevalve body 1001 is as small as one and one-eighth inch square byone-half inch thick. In the preferred embodiment, the valve element 1014is approximately eight times as hard as the seat 1013 so that the seat1013 deforms to fit the valve element 1014 rather than the valve element1014 deforming. In this specification, hardness means compression yieldpoint so that expressions such as eight times as hard mean that it has ayield point eight times higher. Because the materials are hardenedthroughout in the preferred embodiment rather than having only a surfacehardening, the surface hardness is proportional to the yield point.Because the valve element 1014 is substantially harder the the seat, oneor several tight closures of the valve force the valve element into theseat, thereby causing the seat to conform to the spherical surface ofthe valve element. The valve element is not deformed because it is toohard to do so.

To form a sufficiently strong valve element 1014, it is formed in thepreferred embodiment of silicon nitride ceramic. Brittle balls, such asballs of monocrystalline sapphire and polycrystalline aluminum oxideceramic, are generally less desirable and do not have the most usefulhardness characteristics that permit sealing in the valve seat withoutleakage and resistance to scratching or breaking when lifted from theseat in a manner that causes rotation.

The valve element 1014 is one-eighth inch in diameter with a diametraltolerance of 100 microinches and a sphericity tolerance of 16microinches. The close sphericity tolerance is desirable so that, afterthe ball rotates for more or less random reasons when the valve 54A isopen, the sealing surface that is superimposed onto the conical seat1013 by cold flow of the 316 stainless steel (due to the contactpressure or force of the ball 1014) continues to conform to the surfaceof the ball 1014. This conformance in shape with the contact surfacesprevents leaks when the valve 54A is closed. In the preferredembodiment, the ball 1014 has a hardness (compressive strength) of500,000 psi (pounds per square inch).

Fittings for conducting fluids through the valve 54A are threaded intothe female fittings 1002 and 1003 in a manner to be describedhereinafter. Tapered sections or cones of the female fittings 1002 and1003, shown respectively at 1011 and 1005, receive sealing ferrules toseal the connecting tubings protruding from the ferrules in thepassageways 1010 and 1006. The internal threads are shown at 1012 and1004, respectively, to engage the external threads on the correspondingmale fittings.

The valve stem assembly 700 includes an outer stem 1030, an inner stem1027, a hard anti-friction device 1035, a captivating element 1034, aspring 1016, a stepped bushing 1022 and a threaded bushing 1045. Theouter stem 1030 fits rotatably within the threaded bushing 1045 withexternal threads on the outer stem 1030 engaging internal threads on thethreaded bushing 1045.

Beneath the outer stem 1030 is the captivating element 1034 which holdsan upper part of the inner stem 1027. Between the inner stem 1027 at itstop point and the outer stem 1030 is the anti-friction device 1035 whichis a hard ball that contacts the inner stem at a relatively smalllocation and the outer stem 1030 over a wider area to provide aconnection capable of pushing the inner stem 1027 downwardly butunlikely to transmit rotating forces between the outer stem 1030 and theinner stem 1027. The spring 1016 biases the inner packing supportupwardly, compressing washer-shaped packing 1018 against the stem 1027.The inner stem 1027 is supported for up and down movement within thestepped bushing 1022. With this arrangement, rotation of the outer stem1030 causes it to move downwardly within the threaded bushing 1045 tocause the anti-friction device 1035 to press the inner stem 1027downwardly through tightly fitting packing 1018. The inner stem 1027, asit moves downwardly, presses the valve element 1014 into the valve seat1013 and when it moves upwardly, releases the valve element 1014. Thelarger opening of the conical seat 1013 is large enough in diameter andthe recess 1015 is small enough in diameter so that the ball, whenpressed by the face 1023 of stem 1027, will find its way into the seatregardless of fluid flowing outwardly from the larger opening of theseat and regardless of the orientation of the valve with respect togravity.

Above the cavity 1015, is a larger, one-fourth inch diameter,cylindrical recess 1019. In recess 1019, is the Bellville stainlesssteel spring 1016 made of highly work-hardened type 302 stainless steel(Associated Spring Company part number B-0250-013-S), washer-shapedpacking support washer 1017 and semi-hard packing or seal 1018.Bellville spring 1016 is sized to fit loosely within the one-fourth inchdiameter recess 1019 and to fit loosely around the one-eighth inchdiameter internal stem 1027. The spring 1016 bears upwardly on thepacking support washer 1017 and downwardly on the wall of the recess1019. Packing support washer 1017 is made of Armco Nitronic^(R) 60stainless steel to prevent galling due to moving contact with theinternal stem 1027. The annularly-shaped semi-hard seal 1018 ispositioned between the packing support washer 1017 and the bottom of thestepped bushing 1021. It is dimensioned to sealingly fit the cylindricalwall of recess 1019 and is annularly shaped with its central holedimensioned to sealingly fit the circumference of the one-eighth inchdiameter inner stem 1027.

The semi-hard stem seal 1018 is made of DuPont Vespel type SP-211.Vespel is a trademark of DuPont for a temperature-resistantthermosetting polyimide resin reinforced with carbon and internallylubricated with Teflon polytetrafluorethylene powder (Teflon is atrademark of DuPont). Various softer seals made of plain and reinforcedpolytetrafluorethylene (PTFE) were tried, but had inadequate life athigh temperatures and pressures. A seal with a hardness greater than4000 psi, and which retains its hardness better than PTFE at hightemperature, such as Vespel SP-211, is necessary.

The internal stem 1027 is made of age-hardened, cold drawn Type 17-7 PHstainless steel. Internal stem 1027 is guided by stepped bushing 1022made of Nitronic 60 stainless steel. Nitronic 60 is used to preventgalling due to the motion of the contacting internal stem 1027.

There is a distinct relationship between the compressive yield strengthsor hardnesses of the internal stem 1027, the very hard ball 1014 and theconical seat 1013. The ball 1014 must be substantially harder than theface 1023 of stem 1027, and the stem 1027 must be substantially harderthan the seat 1013.

This is because when the valve closes tightly the ball 1014 must deforma relatively large area of the seat (a so-called Hertzian line contact)in order to seal, but the ball 1014 is in contact with a smaller area onthe stem 1027 (a so-called Hertzian point contact). The ball's contactpressure on the stem 1027 is higher than its contact pressure on theseat 1013 because its contact area on the seat 1013 is larger.Nevertheless, the ball 1014 must not too greatly deform into (press toolarge a dimple into) the face 1023 of the stem 1027, or, stem 1027 willswage outwards and interfere with or rub hard on washer 1017. Hence,stem 1027 must have a significantly higher yield point than conical seat1013. Furthermore, ball 1014 should have a significantly higher yieldpoint than stem 1027 so that the permanent contact dimple is on the stemface 1023 and not on the ball 1014. Ball 1014 must retain almost perfectsphericity, as it is free to rotate when the valve is open and if it hasa contact dimple it can produce a leak at the seat 1013 when the valveis closed.

The internal stem 1027 has a neck 1029 and a head 1033 which cooperateswith captivating element 1034 of outer stem 1030. Head 1033 resides incylindrical recess 1070 of outer stem 1030. The anti-friction device orhard ball 1035 transmits thrust from the female conical face 1036 ofouter stem 1030 to the flat surface 1038 at the end of head 1033.

Before assembly of the head 1033 of inner stem 1027 and hard ball 1035into outer stem 1030, captivating element 1034 is straight rather thancurved and extends as a hollow cylinder with its extended interiordiameter being part of the cylindrical recess or cavity 1070. At thefinal part of its assembly process, captivating element 1034 is bent, asshown in the figure, by a spinning or rotary swaging process. Outer stem1030 is made of Type 17-4 PH age-hardened stainless but it not as hardas the interior stem 1027. The 17-7 PH stainless stem 1027 and its face1023 has a hardness of 170,000 psi.

The face 1023 of stem 1027 should have a yield point and hardness atleast 1.3 times higher than the seat 1013 and no more than 0.7 times ashigh as the yield point and hardness of the ball 1014. Screwing the stem1030 counterclockwise relieves the force between the stem face 1023 andthe ball 1014 and the ball 1014 is dislodged by any excess pressurepresent in fluid entering the location 1003, said fluid then exitsthrough location 1002 and is prevented from leaking up through the valvestem area by the spring and fluid pressure loaded semi-hard seal 1018.

Because the yield strength of the 17-7 PH stainless steel at the face1023 of the inner stem 1027 is only about 250,000 psi and the yieldstrength of the silicon nitride ball 1014 is about 500,000 psi, therotation of the stem 1027 would be expected not to have a detrimentaleffect on the very hard ball or element 1014. Nevertheless, rotation ofthe stem 1027 surprisingly puts microscopic scars on the ball 1014 atthe location of the interface between the ball 1014 and the stem end1023. When the ball 1014 rotates later for semi-random reasons when thevalve is opened, and the valve is closed again, these microscopic scarsinterfere with sealing at the interface between the ball 1027 and theconical seat 1013. To avoid these scars, the inner stem 1027 is providedwith an anti-rotation element such as the ball 1035.

In operation, the outer valve stem 1030 may be rotated by any meanswhich may be conveniently coupled to the outer stem 1030 by a pinthrough hole 1046. Clockwise rotation of the stem 1030 causes it to moveinto the valve because of the external threads on outer stem 1030 incontact with internal threads in threaded bushing 1045 which meet in theface of stem 1032. Fine-series one-fourth by 28 threads aresatisfactory. The threaded face of stem 1032 is lubricated with DuPontKrytox^(R) 217 high temperature, high pressure lubricant which iscomposed of perfluoronated polyether oil, low molecular weight powderedpolytetrafluorethylene thickener and powdered molybdenum disulfide highpressure solid lubricant. This lubricant was found to have the best hightemperature resistance of six high pressure, high temperature lubricantstested. The threaded bushing 1045 is made of Nitronic 60 to preventgalling due to the pressure and motion of the threads 1032 of outer stem1030.

As the outer stem 1030 moves inward, so does the inner stem 1027 (FIG.18) because of force transmitted by ball 1035 (FIG. 18). Although outerstem 1030 rotates, inner stem 1027 does not rotate because of theweakness of the rotary frictional force due to the small diameter of thecontact area between the ball 1035 and the top 1038 of the head 1033(FIG. 7) of the inner stem 1027. This weak friction force is notsufficient to overcome the anti-rotation frictional force of the tightlycompressed, seal 1018 (FIG. 18) against the cylindrical surface of theinner stem 1027.

As clockwise rotation of outer stem 1030 continues, eventually the innerstem 1027 is pushed in enough so that its flat end or stem face 1023contacts the very hard valve ball 1014. Further clockwise rotation ofthe outer stem 1030 forces very hard ball 1014 into seat 1013,conformally deforming seat 1013 to fit the ball 1014 and providing atight seal against flow of fluid entering the female fitting 1003 (FIG.18). Fourteen pound inches of torque on stem 1030 provide a tight seal.Conversely, when outer stem 1030 is rotated counterclockwise, outer stem1030 moves outwardly by action of its threads. Captivating element 1034of outer stem 1030 pulls outwardly on the head 1033 of inner stem 1027,disengaging the boss 1023 of inner stem 1027 from tight contract withvalve element or ball 1014. This allows fluid to flow from port 1003 toport 1002 in the valve.

In FIG. 19, there is shown a block circuit diagram of the controlcircuitry 2200 for gear motor 570 (FIGS. 8, 9 and 10) which operatessupercritical fluid supply valve 54A (FIG. 6), gear motor 574 (FIG. 5)which operates extraction valve 50A (FIG. 5), and gear motor 573 (FIG.4) which then operates valve 52A (FIG. 4).

The control circuitry 2200 includes a programmer or other computer 2100,controlling a supply motor circuit 710, an extract motor circuit 712 anda vent motor circuit 714 to control the valves 54A (FIG. 6), 50A (FIG.5) and 52A (FIG. 4), respectively, a reversing switch 716, a drivecircuit 720 and a reverse motor torque circuit 718. The computer 2100 iselectrically connected to the supply motor circuit 710, the extractmotor circuit 712 and the vent motor circuit 714 through conductors2118, 2119 and 2120 electrically connected to output terminals of thecomputer 2100.

The drive, circuit 720 supplies power to a reversing switch 716 that isalso electrically connected to the supply motor circuit 710, the extractmotor circuit 712 and the vent motor circuit 714 to apply power to theselected one of those motors with a polarity that controls the directionof movement of the motors to open a valve or close a valve. Thereversing switch 716 is electrically connected to conductor 2122 from aport 2022 in the computer to activate the reverse direction for closingthe valve. This port is electrically connected to the reverse motortorque circuit 718 which controls the amount of torque in opening thevalve and is for that purpose electrically connected to the drivecircuit 720. A feedback circuit on conductor 2057 is electricallyconnected to the supply motor circuit 710, extract motor circuit 712 andvent motor circuit 714 to provide a feedback signal to the controllerwhich controls the stopping of the motor when the valves close fully.The stop motor signal comes from conductor 2121 from the port 2021 inthe computer or programmer 2100.

In the preferred embodiment, a programmable computer with timingcircuits is utilized. It is the same computer used to operate theembodiment of FIG. 3. However, a manual switch can be used instead whichswitch is connected to a positive voltage supply to energize thecorresponding motor when closed.

The control circuit 2200 includes a supply motor circuit 710, an extractmotor circuit 712, a vent motor circuit 714, a computer or programmer2100, a reversing switch 716, a drive circuit 720 and a reverse motortorque circuit 718. The supply motor circuit 710, extract motor circuit712 and vent motor circuit 714 open and close corresponding ones of thevalves 54A, 50A and 52A.

To control the valves, the computer or programmer 2100 has a pluralityof output conductors that determine which valve is to be moved and thedirection in which it is to be moved. This, in the preferred embodiment,is the computer which operates the extractor 10A (FIG. 3) but may be anytiming device or indeed, instead of a programmer, manual switches may beused to close circuits to 15-volt DC voltages to open and close thevalves as desired by an operator.

In the preferred embodiment, conductors 2118, 2119 and 2120 areconnected to outputs 2018, 2019 and 2020, respectively, of the computeror programmer 2100 and to corresponding ones of the supply motor circuit710, extract motor circuit 712 and vent motor circuit 714 to selectthose valves for opening or closing. A low-level signal on lead 2127attached to computer output port 2021 is electrically connected throughinverter 2026 to the drive circuit 720 to cause it to supply power tothe selected valve through the reversing switch 716 which iselectrically connected to the port 2023 through conductor 2123 to thereversing switch 716 and drive circuit 712.

The reversing switch 716 is electrically connected through conductors2053 and 2051 to each of the supply motor circuits 710, extract motorcircuit 712 and vent motor circuit 714 to supply the drive power theretowith the proper polarity for opening or closing the valves. The reversemotor port 2022 of the computer 2100 is electrically connected throughconductor 2122 to the reverse motor torque circuit 718 and to thereversing switch 716 to select the polarity of electrical power tosupply through conductors 2053 and 2051 to the selected one of thesupply motor circuit 710, extract motor circuit 712 and vent motorcircuit 714 to cause the motor to move the valve into the open positionor closed position.

A torque adjustment feedback circuit connected to each of the motorcircuits 710, 712 and 714 generates a potential which is fed backthrough conductor 2057 to the drive circuit 720, and in conjunction withthe current sense signal on lead 2123 and the stop motor conductor 2121from the computer 2100, determines when the motor should stop at theclose valve position. The setpoint of this meter stopping torque may beset at the motor (FIG. 20) and may advantageously be programmed into thecomputer 2100 (FIG. 19). The reverse motor torque circuit increases thepower supplied to the drive circuit 720 when the motors are moving inthe direction that opens the valve to overcome overtightening due todifferential expansion due to a temperature change since the valve waslast closed, which may tend to keep the valve closed and to ensureopening of the valve on command.

In FIG. 20, there is shown a schematic circuit diagram of the supplymotor circuit 710, extract motor circuit 712 and vent motor circuit 714having gear motor 570, gear motor 574 and gear motor 573, respectively.Gear motor 570 is electrically selected by relay 2000, gear motor 574 iselectrically selected by relay 2001 and gear motor 573 is electricallyselected by relay 2002. Gear motor 570 controls or regulates theposition (in this case, open or closed) of valve 54A (FIG. 6), gearmotor 574 similarly controls valve 50A (FIG. 5) and gear motor 573similarly controls valve 52A (FIG. 4).

The computer or programmable controller 2100 is the same computercontroller or programmable controller that automates the other functionsof the automatic extraction apparatus shown in FIG. 3. This conventionalcomputer or programmable controller 2100 may be conventionallyprogrammed to carry out any one of a variety of extraction protocols,including control of the valves. Computer 2100 has output ports 2018,2019, 2020, 2021 and 2022 shown in FIG. 11. It also has input port 2023.Output port 2018 controls relay 2000 through inverter 2015. All of theinverters used in FIG. 11 are Type 2803 devices with open collectoroutputs. Output port 2019 controls relay 2001 through inverter 2016.Output port 2020 controls relay 2002 through inverter 2017.

In FIG. 21, there is shown a schematic circuit diagram of the reversingswitch 716, reverse motor torque circuit 718 and drive circuit 720 ofthe control circuitry 2200. As best shown in this circuit, the outputport 2022 controls relay 2003, of the reversing switch 716, throughinverter 2027. Relay 2003 has its contacts wired in a conventionaldouble-pole double-throw reversing circuit. It is used to reverse thevoltage applied to whichever of the three gear motors is selected byrelays 2000, 2001 or 2002 (FIG. 12).

To control torque, the control circuitry 2200 includes an operationalamplifier 2036 and a power field effect transistor 2029 that providecurrent control (and therefore torque control) of the selected gearmotor. Operational amplifier 2036 is a type 324 and power FET 2029 is aType MTP12N06. Contacts 2024 of relay 2003 connect the drain 2050 of thepower FET 2029 to one of the electrical terminals of the three gearmotors 570 (FIG. 6), 574 (FIG. 5) and 573 (FIG. 4), and the motorselected by relay 2000, 2001 or 2002 (FIG. 12). Therefore, motor currentflows through power FET 2029 and through current sensing resistor 2030to circuit common.

The voltage drop across current sensing resistor 2030 is applied to theinverting input 2045 of operational amplifier 2036. The output 2043 ofthe operational amplifier 2036 is led through resistor 2034 to the gate2048 of the power FET 2029. Resistors 2030 and 2032, the operationalamplifier 2036 and the power FET 2029 provide a negative feedback orservo loop which is used to set the maximum current (and therefore themaximum torque or torque limit) of the gear motors. Resistor 2033 isconnected between the output 2043 of the operational amplifier 2036 andsets the gain or proportional band of the servo loop.

The current setpoint is established by the voltage at the noninvertinginput 2044, of the operational amplifier 2036. A positive 2.5 voltsreference voltage is applied to terminal 2042 and is led to thenoninverting input through resistor 2040. The same relays 2000, 2001 and2002 that select one of the three gear motors 570, 574 and 573. (FIG.12) also simultaneously select an adjustable resistor corresponding toeach gear motor. Adjustable resistor 2018 corresponds to gear motor 570,adjustable resistor 2019 corresponds to gear motor 574, and adjustableresistor 2020 corresponds to gear motor 573. Different nominally similargear motors have somewhat different current-to-torque characteristicsand the torque limit must be set separately for each gear motor.

Variable resistances 2018, 2019 and 2020 corresponding respectively togear motors 570, 574 and 573 are respectively selected by relay contacts2006, 2009 or 2011. The contacts 2006, 2009 and 2011 connect theselected variable resistance to conductor 2057 which is connected to theresistor 2040 and the noninverting terminal 2044 of the amplifier 2036.The voltage at inverting input 2045 equals the voltage at noninvertinginput 2044 when current or torque limiting is taking place.

The voltage across resistor 2030 is nearly the same as the voltage atthe inverting input 2045, so changing the resistance of the variableresistances 2018, 2019 or 2020 during current limiting, varies thevoltage across resistor 2030, and varies the limiting current throughresistor 2030, which is the same as the current through the selectedgear motor. The output port 2022 of the computer 2100 (FIG. 11) is alsoconnected to the gate electrode 2046 of field effect transistor 2038.The source 2060 of the field effect transistor 2038 is connected tocircuit common and its drain is connected to the inverting input 2045 ofthe operational amplifier 2036 through resistor 2037.

When the computer operates a selected motor in the reverse(valve-opening) direction, the voltage level at output port 2022 (FIG.11) goes high, turning on field effect transistor 2038 through its gate2046. This effectively connects the resistor 2037 between circuit commonand the inverting input 2045 of the operational amplifier 2036. Resistor2037 is approximately twice the value of resistor 2032, so it requires1.5 times as much voltage across (and current through) resistor 2030 andthe selected gear motor to bring the voltage at inverting input 2045 upto the voltage at noninverting input 2044.

The effect is to increase the torque limit by a factor of about 1.5 whenthe valve is opening as compared to when the valve is closing. Thisensures that the valve does not stick if the opening torque is greaterthan the closing torque. It is surprising that such a jam can occur asit is known from experience that it takes less torque to reopen a valvethan to close it. However, it is believed the reason for high openingtorque is differential thermal contraction occurring when the valve isclosed at a high temperature and then later opened at a significantlylower temperature.

It is desirable to shut off and turn on power to the gear motors 570,574 and 573 (FIG. 12) by means other than the selector relays 2000, 2001and 2002, and also to shut off power during a change of state ofreversing relay 2003. It is desirable because these relays have longerlife if their contacts switch (change state) at a time when no currentis going through their contacts and because solid state power switchinggenerates less electrical noise.

To this end the output port 2021 of computer 2100 (FIG. 11) provides alogic high level to shut off power FET 2029 through inverter 2026. Ahigh level signal at output port 2021 (FIG. 11) is inverted by inverter2026 and the resulting low level voltage is applied to the gate 2048 ofpower FET 2029, turning off the power FET 2029 and interrupting power tocontacts 2024 and 2025 of relay 2003, contacts 2005 of relay 2000,contacts 2008 of relay 2001 and contacts 2010 of relay 2002. Thecomputer 2100 (FIG. 7) is programmed so that the voltage level at outputport 2021 (FIG. 11) goes high (power off) before the change of state ofevery relay and then goes low (power on) after a relay change of state.

When a valve is closing, the torque impressed on its gear motor startsto rise and the current through the gear motor starts to rise when theball 1014 (FIG. 7) is forced into the conformal seat 1013. When thetorque and current rise to the limit point described earlier, thevoltage at the output 2043 of operational amplifier 2036 decreases. Thisdecreased voltage is applied to gate 2048 of power FET 2029, andtherefore the power FET 2029 starts to turn off. When this happens, thevoltage at its drain 2050 and on the conductor 2055 starts to rise,causing current to flow through resistor 2035. Resistor 2041 forms avoltage divider with resistor 2035. The voltage division ratio isselected to indicate a torque limiting condition when the voltage onconductor 2055 produces a voltage at input port 2023 of computer 2100(FIG. 11) which is equal to the logic level at that input port. Thissignals the computer 2100 that the valve has been closed.

Operation for a simple extraction procedure under programmable controlis as follows with valves 54A (FIG. 6), 50A (FIG. 5) and 52A (FIG. 4)closed. Under computer control, gear motor 454 (FIG. 4) rotates highspeed screw 476, elevating cartridge 30A into the extraction chamberwithin pressure vessel 24A (FIG. 4). The cartridge 30A positioned withinthe extraction chamber is shown in FIG. 6. Gear motor 600 drives lockingmechanism 606 under computer control, effectively locking the extractioncartridge 30A within the extraction chamber (FIG. 6). The logic level atoutput port 2021 of computer 2100 (FIG. 19) has been high, shutting offpower to all relay contacts. Then the logic level at port 2018 ofcomputer 2100 (FIG. 19) goes high, turning on the coil of relay 2000 byaction of the inverter 2015 (FIG. 20). Simultaneously, output port 2022(FIG. 19) goes high activating relay 2003 (FIG. 21) through inverter2027.

This places the contacts 2024 and 2025 of relay 2003 (FIG. 21) in theopposite position from that shown in FIG. 21. This is the reverse orvalve-opening position. Simultaneously, the gate 2046 of FET 2038 goeshigh, turning on FET 2038.

After a fraction of a second, the logic level at port 2021 (FIG. 19)goes low, enabling the relay contact circuits by allowing power FET 2029to turn on. A positive 15 volts at terminal 2070 is applied throughcontacts 2025 to place positive voltage on the bottom terminals (FIG.19) of the gear motors 570, 574 and 573 (FIG. 20) which enables them tooperate in reverse or in the direction which opens their associatedvalves. Positive voltage applied to the top terminals of these threemotors enables closing of their respective valves.

Relay 2000 then selects the upper terminal of gear motor 570 throughconductor 2052, contacts 2005 and conductors 2054 and 2053 (FIG. 20).Lead 2053 is connected to conductor 2055 through contacts 2024 sincerelay 2003 is activated. Lead 2055 is connected to the drain of powerFET 2029 in the current limiting circuit. Since the motor requires lessthan the limiting current to open, it runs in the reverse(valve-opening) direction at a continuous speed of about 16 rpm, openingvalve 54A (FIG. 6). After three seconds of such running and thecorresponding opening of valve 54A, the computer 2100 causes output port2021 (FIG. 19) to go high putting a low on the gate of power fieldeffect resistor 2029 through inverter 2026 (FIG. 21). This stops currentthrough the relay contacts and motor 570 (FIG. 20), and valve 54A (FIG.7) remains open with the motor stopped. After a fraction of a second,port 2018 (FIG. 19) goes low turning off the relay 2000 which hadselected motor 570 (FIG. 20).

The computer 2100 (FIG. 19) is programmed so a signal at its output port2021 (FIG. 19) always shuts off the power FET current source transistor2029 (FIG. 21) a fraction of a second before any of the relays 2000,2001, 2002 (FIG. 20) or 2003 FIG. 21) change state. The computer 2100 isalso programmed so that a signal at port 2021 re-enables the power FET2029 a fraction of a second after a single or a group of simultaneousrelay state changes, if power is needed at that time. Thus, none ofthese relays are required to switch any active current or power andtheir life is thereby prolonged. The operation of this protectivefeature is performed each time before and after each change of state ofany of the relays.

In accordance with the above, gear motor 570 (FIG. 20) has opened valve54A. This valve supplies supercritical fluid from a fluid line (notshown) attached to outlet port 308 of pumping system 1100 (FIG. 11) orpump 780 (FIG. 11); through fluid leads, lines or tubings 58A (FIG. 6)and 60A (FIG. 1) to the interior of the extraction chamber 24 (FIGS. 1,2 and 3) and extraction cartridge 30A (FIG. 6). Then, computer outputport 2019 (FIG. 19) goes high selecting relay 2001 through inverter 2016(FIG. 20). Relay 2003 (FIG. 21) is still activated. Contacts 2008 ofrelay 2001 (FIG. 20) connect the upper conductor of motor 574 (FIG. 20)to conductor 2055 through contacts 2024 of relay 2003 (FIG. 21). Thiscauses gear motor 574 to open valve 50A (FIG. 5). Valve 50A connects theoutlet of the extraction cartridge 30A (FIG. 6) to restrictor tube 66A(FIG. 5) which leads to extractant collection vessel 98A. Three secondsafter valve 50A starts to open, the computer 2100 causes the level atport 2019 (FIG. 11) to go low and motor 574 stops opening valve 50A,leaving valve 50A open.

Restrictor 66A (FIGS. 4 and 5) depressurizes supercritical fluid fromthe high pressure in extraction cartridge 30A (FIG. 6) to the lowerpressure in collection vessel 98A (FIG. 4). The pressure in collectionvessel 98A is usually comparatively close to atmospheric pressure andthe supercritical fluid carrying dissolved sample usually has changed toa gas carrying entrained sample as it exits the restrictor 66A.Supercritical extraction of the contents of extraction cartridge 30Atakes place as previously described.

A programmable timer within computer 2100 (FIG. 19) is set to thedesired duration of the supercritical extraction. If the timer is setfor ten minutes, then ten minutes after valve 50A (FIG. 5) opens, theextraction is complete. Output port 2022 of computer 2100 (FIG. 11) goeslow, de-energizing relay 2003 through inverter 2027 (FIG. 13).De-energized contacts 2024 and 2025 of relay 2003 (FIG. 21) reverse thevoltage to the gear motors 570, 574 and 573 (FIG. 20), enabling the gearmotors to turn in the forward (valve-closing) direction. Field effecttransistor 2038 turns off because of the low voltage on its gate 2046(FIG. 13). Simultaneously, the computer causes its output port 2018(FIG. 11) to go high, energizing relay 2000 through inverter 2015 (FIG.20). Relay 2000 connects the upper terminal of gear motor 570 throughconductor 2052, the relay contacts 2005, conductor 2054, conductor 2053(FIG. 20), contacts 2025 of relay 2003 (FIG. 21) and to a positive 15volt source at terminal 2070 (FIG. 20).

The lower terminal of gear motor 570 is connected through conductor 2051(FIG. 20) to contacts 2024, conductor 2055 and drain 2050 of fieldeffect transistor 2029 (FIG. 21) and from the source of the field effecttransistor 2029 to resistor 2030. Contacts 2006 of relay 2000 connectvariable resistance 2018 to conductor 2057 (FIG. 20) and then tononinverting input 2044 of operational amplifier 2036 (FIG. 21). Gearmotor 507 now runs in the forward (valve-closing) direction with acurrent or torque limit set by variable resistance 2018 (FIG. 20).

As the valve closes tightly, pressing ball 1014 into conformal seat 1013(FIG. 7), the motor torque and motor current increases, increasing thevoltage across current sensing resistor 2030 (FIG. 21). As the torqueand current increase a preset amount, the voltage on conductor 2055(FIG. 21) becomes sufficiently high to reach the logic level of computerinput port 2023 (FIG. 19) through the voltage divider composed ofresistors 2035 and 2041 (FIG. 21). This causes the computer 2100 (FIG.19) to bring the voltage at its output port 2018 low, de-energizingrelay 2000 (FIG. 20). Then the computer brings the voltage at outputport 2019 high. This energizes relay 2001 through inverter 2016,selecting gear motor 574 (which is coupled to valve 50A) and variableresistance 2014. Motor 574 rotates in the forward (valve-closing)direction closing the valve 50A (FIG. 5).

When the valve 50A (FIG. 5) is closed, the motor current increases untilthe voltage across current sensing resistor 2030 is approximately equalto the voltage at inverting input terminal 2045 of operational amplifier2036 (FIG. 21), which is set by variable resistance 2019 associated withmotor 574 (FIG. 20). This causes current and torque limiting which alsocauses the voltage of conductor 2055 (FIG. 21) to rise, in turn causingthe voltage at current sensing input port 2023 (FIG. 11) to rise throughthe voltage divider comprised of resistors 2035 and 2041 (FIG. 13).

When the voltage at input port 2023 was the logic level of the computer2100 (FIG. 19), the computer 2100 shuts off motor 574 (FIG. 20) at itspredetermined torque limit. The voltage at output port 2019 goes low,de-energizing relay 2003 (FIG. 13) through inverter 2016 (FIG. 20).Output port 2022 (FIG. 11) goes high, energizing relay 2003 throughinverter 2027 (FIG. 21). Energized contacts 2024 and 2025 (FIG. 21)enable gear motor 573 to open its high energizing relay 2002 throughinverter 2017 (FIG. 20) contacts 2010 and 2011 of relay 2002 select gearmotor 573 connected to valve 52A (FIG. 4) and select variable resistance2020 (FIG. 20) which sets the torque and current limit for gear motor573. Gear motor 573 runs in the reverse (valve-opening) direction forthree seconds opening valve 52A, which vents or discharges the pressurein the interior pressure vessel 24A and in extraction cartridge 30A(FIGS. 4 and 6).

After a suitable delay time to allow the pressure to reach anear-atmospheric value, gear motor 600 (FIG. 6) operates in reverse,unlocking the locking mechanism 606 (FIG. 6) under computer control. Thegear motor 454 (FIG. 4) then rotates in reverse, causing high speedscrew 476 to lower cartridge 30A from the extraction chamber withinextraction vessel 24A.

Controlling the closing of the valves so that the valve stem motionstops when a torque limit is reached at the gear motor, is moredesirable than closing the valve until a position limit is reached. Thistorque feedback limit control provides just enough force to close thevalve. On the other hand, position control tends to either underclosethe valve so that it leaks or overdose the valve so that excessunnecessary force causes unneeded wear of the seat.

The algorithm used to control the gear motor and open and close thecorresponding valve is particularly useful as it is self-adjustingregardless of how far the inner stem 1027 forces the ball 1014 into seat1013 (FIG. 18). Since the valve-opening torque is greater than theclosing torque, the valve cannot stick closed and cause an erroneous"valve-open" condition within the computer or programmer. With repeatedoperation, the ball 1014 may be forced further and further into conicalseat 1013 as the ball 1014 deforms a larger and larger area of theconical seat 1013 into a shape that conforms with the ball 1014. Inclosing the valve 54A, the gear motor always also forces the ball 1014tightly into the seat 1013, shutting off the flow since the gear motorcontinues to run until attaining the torque limit which indiates leaktight seating of the ball 1014.

During opening of the valve 54A, the motor runs for a predetermined timewhich is equivalent to a predetermined angular rotation. This is becausethe motor runs in reverse at constant speed after the first fraction ofone-thousandth of an inch of stroke of the inner stem 1027 (FIG. 18)while the stem 1027 is still applying force to the ball 1014 (FIG. 18).During all this time the motor runs with excess torque and is not undulyslowed down because the high logic level at computer output port 2022(FIG. 11) is applied to the gate 2046 turning on field effect transistor2038 (FIG. 13). As described previously, this sets a torque limitconsiderably higher than that necessary to loosen the ball 1014 from itsseat 1013.

In operation, a program is entered into the control panel 410 (FIG. 4).This program is then stored in controller 450 (FIG. 4) and controlssample changing, fraction collection, static and/or dynamic extractions,fluid pressure, the steps or ramps of pressure, the supercritical fluidtemperature, the elevation of the sample cartridge from the sampler reelup to the extraction chamber and return back to the sampler reel afterextraction, locking and unlocking of the extraction chamber andoperation of the three motor-operated valves in the manner describedabove to automatically duplicate the hand-operated functions of manualembodiments. In the alternative, the operations may be initiated fromthe keyboard by manually closing circuits to the motors as required toperform the desired sequence.

At the start of an extraction cycle, the extraction fluid valve 54A(FIGS. 6 and 7), purge valve 50A (FIG. 5), and the extractant valve 52A(FIG. 4) are closed. The sample reel 430 (FIG. 3) brings a selectedextraction cartridge 30A into position under the extraction chamber 618(FIG. 4). The extraction sample cartridge 30A within a sleeve 436 (FIG.3) on reel 430 is positioned above the single hole 464 in the disk 462(FIG. 4) and is supported on a spring-loaded support block 482 withinthe top of the piston 32A (FIG. 4).

To move the sample cartridge 30A (FIGS. 4 and 6) into the extractionchamber 618 (FIG. 4), the gear motor 454 (FIG. 4) causes the screw 476,piston 32A and cartridge 30A (FIGS. 4 and 6) to rise to the positionshown in FIG. 6, inserting cartridge 30A and piston 32A into thepressure vessel 24A.

To lock the sample cartridge 30A in position, the gear motor 600 drivesthe pin 606 through the hole 609 in the pressure vessel 24A through thehole 610 in the piston 32A and through the hole 612 in the pressurevessel 24A (FIG. 6). This locks the piston into position within thepressure vessel 24A.

To remove extractant, the spring 201A under the block 482 (FIG. 4 )forces the block 482 to push the sample cartridge 30A up against thebottom of the fitting 46A (FIG. 4). The gear motor 552 lowers the arm560 carrying the restrictor tube 66A and the rack 406 (FIG. 3) into theposition shown in FIG. 5, puncturing the cap 550 on the collection tube98A. Alternatively, the collection tube 98A may be automatically raisedto the restrictor tube 98A. The gear motor 570 (FIGS. 9, 10 and 12)rotates, opening the extraction fluid valve 54A (FIG. 6), admittingextraction fluid from a tube (not shown) connected to the outlet port308 of pumping system 1100 (FIG. 11) or pump 780 (FIG. 12), through theheat exchanger 40A, tube 60A and the fitting 42A (FIG. 4).

The extraction fluid flowing through the fitting 42A enters the bottomof the extraction cartridge 30A (FIG. 4) and permeates the sample withinit. If it is suspected that the outside cartridge 30A may becontaminated, the purge valve 52A is opened at this time under thecontrol of the gear motor 573 (FIG. 4). This purges or flushes the spacebetween the outer wall of the sample cartridge 30A and the inner wall ofthe pressure vessel 24A. Flushing fluid leaves the extraction chamber618 outside of the cartridge 30A through the purge fitting 44A, tube62A, Tee-joint tube 542, tube 620 (FIG. 4), Tee-joint tube 544, tube 548and vent port 546 (FIG. 4).

After purging, the gear motor 573 closes the purge valve 52A (FIG. 4),terminating the purge operation. At this time, the controller 450 (FIG.3) activates the gear motor 574 (FIG. 5) which opens the extractantvalve 50A. Extractant fluid flows through the cartridge 30A, extractsmaterial from the sample within the cartridge 30A, flows through thefitting 46A (FIG. 4), tubing 62A (FIG. 4), extractant valve 50A (FIG.5), and to the restrictor tube 66A (FIG. 4). The restrictor tube 66A hasa capillary bore of a small enough diameter to maintain the desiredextraction pressure at the desired extraction fluid flow rate.

In case the extraction cartridge 30A (FIGS. 16 and 18) is not completelyfull of sample, it is beneficial to flow the extractant fluid downwardthrough the cartridge 30A instead of upwards as in the foregoingexample. Downward flow of extractant is accomplished by permitting theextractant to flow into the cartridge 30A through fitting 46A (FIG. 4)and from the cartridge 30A through fitting plug 32A (FIG. 4) and thefitting 42A (FIG. 4).

After extraction is complete and the extractant is collected in thetrapping fluid 104A within the vial 98A (FIG. 5), the gear motor 570(FIG. 6) shuts the extraction fluid valve 54A (FIG. 6). The gear motor573 opens the purge valve 52A rapidly discharging the pressure and theextraction chamber 618 (FIG. 4). The gear motor 574 closes theextractant valve 50A and the gear motor 552 raises the arm 560 andrestrictor tubing 66A and exhaust tubing 110A (FIG. 5). The gear motor600 withdraws pin 606 from the holes 609, 610 and 612 in the pressurevessel 24A and the piston 32A (FIG. 6).

After the piston 32A has been unlocked, the gear motor 573 (FIG. 4)lowers the piston and sample cartridge 30A so that the sample cartridge30A is lowered from being within the extraction volume 618 (FIG. 4) tobeing within the sleeve 436 of the sample reel 430 (FIG. 3). The gearmotor 570 closes the purge valve 54A (FIG. 6).

After the valves have been closed and the sample cartridge 30A (FIGS. 4and 6) returned to the sample reel, the sample reel 430 and the fractioncollector reel 440 (FIG. 3) advance to bring another sample cartridge inanother fraction collector vial into position.

As can be understood from the above description, the supercriticalextraction technique has several advantages, such as for example: (1) itis more convenient than prior art extractors; (2) it automates thesample injection and fraction collection part of the extraction processas well as automating the extraction itself; (3) it is smaller and morecompact because of the air-thermoelectric cooling the pumphead and theinlet fluid separately and simultaneously being water cooled; (4) it mayhave a reasonably high flow rate; (5) seal life is lengthened byimproving the alignment of the plunger within the seal; and (6) fluidvolume leaving the pump is precisely measured.

Although a preferred embodiment of the invention has been described insome detail, many modifications and variations of the preferred,embodiment can be made without deviating from the invention. Therefore,it is to be understood that within the scope of the appended claims theinvention may be practiced other than as specifically described.

We claim:
 1. A system for pumping and for measuring the outlet flow of a very compressible fluid at a predetermined flow rate and a high pressure, comprising:a reciprocating pump having a cyclic period of fluid delivery with a start and a finish; said reciprocating pump including a pumping chamber means adapted to contain fluid at a predetermined pressure, a movable volume-displacement means which moves cyclicly between two extreme positions for displacing a maximum and a minimum volume from the pumping chamber; an inlet check valve, an outlet valve and an outlet line carrying the outlet fluid flow; a flow-onset sensing means for transducing a signal related to a start of high pressure fluid flow to a first electric signal; a sensing means for detecting the times at which the said displacement means is substantially located at one of its said extreme positions during each of the said cycles of movement; a differentiating means for operating upon the first electric signal to produce a second electric signal dependent on rates of change in the first electric signal; a detection means for sensing the second electric signal and for detecting a change in the rate of change of the pressure during each of said cyclic motions of the said displacement means; a switching means turned on for a time duration by the detection means after the start of the cyclic period of fluid delivery and turned off by said second electric signal; said displacement means having a position transducer whose output is a third electric signal proportional to displacement within the said pumping chamber; and a time integral means which cyclicly integrates the said third electric signal during the time duration wherein the integral of the third signal is proportional to the outlet flow of the pump.
 2. A system according to claim 1 in which a utilization means controls the predetermined flow rate of the fluid.
 3. A system according to claim 1 wherein:the flow-onset sensing means includes a pressure transducer means for sensing the said fluid pressure within the pumping chamber; the differentiating means is a single differentiator, producing a first derivative signal; the detection means includes means for detecting a change in the first derivative signal from a high positive level to a lower positive level, and; the sensing means includes means for detecting the time at which the displacement means displaces substantially the said maximum volume from the pumping chamber.
 4. A system according to claim 3 wherein:the pressure transducer senses the fluid pressure within the outlet line; the differentiating means is a single differentiator that produces a second electric signal proportional to the first derivative of a said pressure within the outlet line, and; the sensing means includes means for detecting the time at which the displacement means displaces substantially at the said maximum volume from the pumping chamber.
 5. A system according to claim 4 wherein the said detection means detects a change in the first derivative from a negative level to a positive level.
 6. A system according to claim 1 in which the sensing means is a pressure sensor and the signal is a pressure signal.
 7. A system according to claim 1 in which the sensing means is a flow meter.
 8. A system according to claim 1 wherein:the flow-onset sensing means includes a pressure transducer wherein the pressure transducer senses the fluid pressure within the pumping chamber, the differentiating means is a double differentiator providing a first and second derivative; and, the detection means detects a change in the second derivative from a zero level to a negative level, and; the sensing means detects the time at which the displacement means displaces substantially the said maximum volume from the pumping chamber.
 9. A system according to claim 8 wherein:the pressure transducer senses the said fluid pressure within the pumping chamber; the differentiating means is a single differentiator which produces a second electric signal proportional to a first derivative of said pressure within the pumping chamber and; the said detection means detects a change from the said first derivative from a small positive to a large negative value to determine the finish of fluid delivery and detects a change in the first derivative from a large positive value to a smaller positive value to determine the finish of fluid delivery.
 10. A system for pumping and for measuring the outlet flow of a very compressible fluid from a high pressure pump, comprising:a reciprocating pump having a cyclic period of fluid delivery wherein the period of flow delivery has a start and a finish, a pumping chamber containing fluid at a pressure, a movable displacement means which moves cyclicly between two extreme positions in the pumping chamber, one of said extreme positions corresponding to the finish of the cyclic period of fluid delivery, an inlet check valve, an outlet check valve and an outlet line carrying the outlet flow of fluid; a pressure transducer means for transducing a characteristic indicating the start of fluid delivery pressure of the said high pressure fluid to a first electric signal; a differentiating means for operating upon the first electric signal to produce a second electric signal dependent on rates of change in the first electric signal; detection means for sensing the said second electric signal and for detecting changes in a rate of change of pumping by the high pressure pump during the said cyclic motions of the displacement means, whereby changes of the second electric signal indicate the start and finish of fluid delivery during a cycle of the pump, wherein a start of fluid delivery is determined by a change in the rate of change of the second signal after a the said finish of fluid delivery and a finish of fluid delivery is determined by an event that takes place after a start of said fluid delivery; switch means controlled by said detection means to be turned on at said start of the period of fluid delivery and turned off at said finish of the period of fluid delivery; said displacement means having a position transducer whose output is a third electric signal proportional to displacement within the pumping chamber; a time integral means which cyclicly integrates the third electric signal between time limits set by the time period during which the switch means is on, and; a utilization means which utilizes the time integral as an amount proportional to the outlet flow of fluid from the pump.
 11. A system according to claim 10 in which the event is a change in the rate of change of the second electrical signal.
 12. A system according to claim 10 further including a sensing means that senses one of the two extreme positions, and the event is the sensing of the one of the two extreme position of the displacement means that corresponds to the finish of flow delivery.
 13. A system according to claim 10 wherein:the pressure transducer means senses the said fluid pressure in the outlet line; the differentiating means being a single differentiator which produces a first electric signal porportional to the first derivative of the pressure within the outlet line and; the sensing means detects a change in said first derivative from a negative value to a positive value to determine a start of fluid delivery and detects a change in said first derivative from a postive value to a negative value to determine a finish of fluid delivery.
 14. A method of pumping and measuring the outlet flow of a very compressible fluid used for supercritical extractions, comprising the steps of:pumping fluid with a reciprocating pump having a plurality of cyclic periods of fluid delivery each of which has a start and a finish, a pumping chamber containing liquid at a pressure, a movable volume-displacement means which has a cyclic motion between two extreme positions wherein a maximum and a minimum volume are displaced from the pumping chamber; generating a signal with a pressure transducer means which transduces the pressure of high pressure fluid flow to a first electric signal; detecting the times at which the said displacement means is substantially located at one its said extreme positions during each of the cyclic motions; differentiating said first electric signal with a differentiating means to produce a second electric signal dependent on rates of change in the said first electric signal; sensing the second electric signal with a sensing means; detecting a change in the rate of change of the said high pressure with a detection means during each of said cyclic motions of the said displacement means; turning on a switching means for a time duration upon the detection the second electric signal after the start of the period of fluid delivery and turning off the switching means at the end of the time duration; generating a third electric signal with a position transducer, the output of which is proportional to displacement within the said pumping chamber; cyclicly integrating the third electric signal between time limits set by the said time duration during which the said switching means is on wherein an integral of the third electric signal is obtained; and utilizing the integral of the third electric signal as an amount proportional to the outlet flow of the pump.
 15. A method according to claim 14 wherein:the pressure transducer means senses the said fluid pressure within the pumping chamber; the differentiating means produces a first derivative signal; the detection means detects a change in the said first derivative signal from a high positive level to a lower positive level; and the sensing means detects the time at which the displacement means displaces substantially the said maximum volume from the pumping chamber.
 16. A method according to claim 14 wherein:the pressure transducer means senses the said fluid pressure within the pumping chamber; double differentiating the signal; detecting a change in the second derivative from a zero level to a negative level, and; detecting the time at which the displacement means displaces substantially the said maximum volume from the pumping chamber.
 17. A method according to claim 14 wherein the pressure transducer senses the said fluid pressure within the outlet line;the said differentiating means producing a second electric signal proportional to the first derivative of the said pressure within the outlet line, and; detecting the time at which the displacement means displaces substantially at the said maximum volume from the pumping chamber.
 18. A method according to claim 14 wherein the said detection means detects a change in the said first derivative from a negative level to a positive level.
 19. A method for pumping and measuring the outlet flow of a very compressible fluid used for supercritical extraction, comprising the steps of:pumping fluid with a reciprocating pump having a plurality of cyclic periods of fluid delivery each of which has a start and a finish; said step of pumping including the substeps of moving a movable displacement means which has cyclic motions between two extreme positions in a pumping chamber, to pump into an outlet line carrying the outlet flow; transducing the pressure of the said high pressure fluid to a first electric signal; producing a second electric signal dependent on rates of change in the said first electric signal; sensing the said second electric signal and detecting changes in the rate of change of the said high pressure during the said cyclic motions of the said displacement means, wherein the changes in the second electric signal indicate the start and finish of fluid delivery during a cycle of the pump, determining said start of fluid delivery by a change in the rate of change of the said second signal after a said finish of fluid delivery and determining said finish of fluid delivery by a change in the rate of change of the said second signal after a start of said fluid delivery; turning on switch means in response to said detection means at the said start of the period of fluid delivery and turning off the switch means at the finish of the period of fluid delivery; generating a second electric signal on said displacement means with a position transduceer proportional to displacement within the said pumping chamber; cyclicly integrating the second electric signal between time limits set by the time period during which the said switch means is on, and; utilizing the said integral as an amount proportional to the outlet flow of the pump.
 20. A method according to claim 19 further comprising the steps of:sensing the fluid pressure within the pumping chamber and producing a second electric signal proportional to the first derivative of said pressure within the pumping chamber and; detecting a change from the said first derivative from a small positive to a large negative value to determine the finish of fluid delivery; and detecting a change in the said first derivative from a large positive value to a smaller positive value to determine the finish of fluid delivery.
 21. A method according to claim 20 further comprising the steps of:sensing said fluid pressure in the outlet line; producing a first electric signal proportional to the first derivative of the fluid pressure within the outlet line by differentiating said pressure and; detecting a change in the said first derivative from a negative value to a positive value for determining a start of fluid delivery and detecting a change in the said first derivative from a positive value to a negative value for determining a finish of fluid delivery. 